Pavement design supplement (PDF, 534 KB)

Pavement Design Supplement Supplement to ‘Part 2: Pavement Structural Design’ of the Austroads Guide to Pavement Technology July 2018

Pavement Design Supplement, Transport and Main Roads, July 2018

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© State of Queensland (Department of Transport and Main Roads) 2018

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Pavement Design Supplement, Transport and Main Roads, July 2018 i

About this document

The Queensland Department of Transport and Main Roads adopts the fundamental pavement design principles in Part 2: Pavement Structural Design of the Austroads Guide to Pavement Technology (Austroads, 2017), hereafter referred to as AGPT02.

Transport and Main Roads has published this Pavement Design Supplement (‘this supplement’), for use in departmental projects, to complement the design guidance provided by Austroads, such as for Queensland’s local materials, environment, loadings and pavement performance. Therefore, this supplement generally does not repeat the guidance already provided in AGPT02, and pavement designers completing designs for Transport and Main Roads works must use this supplement in conjunction with AGPT02, as well as any other project-specific requirements.

This edition of the supplement replaces the 2017 Pavement Design Supplement. The supplement has been updated primarily to:

• align with the 2017 version of AGPT02

• align with the new specifications MRTS10 Plant-Mixed Lightly Bound Pavements and MRTS32 High Modulus Asphalt (EME2), and the updated specifications MRTS05 Unbound Pavements, MRTS11 Sprayed Bituminous Treatments (Excluding Emulsion) and MRTS18 Polymer Modified Binder (including Crumb Rubber)

• align with the new Transport and Main Roads Technical Notes TN171 Use of High Standard Granular (HSG) Bases in Heavy Duty Unbound Granular Pavements and TN175 Selection and Design of Sprayed Bituminous Treatments

• introduce a minimum support condition for bound layers in heavily trafficked pavements

• introduce an improved method for characterisation of selected subgrade materials for mechanistic-empirical design of flexible pavements

• include references to recycled material blends, as specified in MRTS35 Recycled Materials for Pavements, for use in unbound, lightly bound and heavily bound (cemented) pavement layers

• include High Modulus Asphalt (EME2), as previously published in Transport and Main Roads Technical Note TN142 High Modulus Asphalt (EME2) Pavement Design

• introduce an "extreme" category of expansive subgrade material and include guidance for cover over very highly expansive subgrades

• separate guidance on soft subgrade treatments to better distinguish between construction requirements and design conditions

• include guidance on the selection and derivation of traffic load distributions.

This supplement is not a prescriptive standard, rather it is intended to be a guide for professional, trained, experienced and knowledgeable pavement designers who:

• work within the confines of government policies, guidelines and road network requirements

• are aware of, assess and apply risk management and budgetary constraints to the road system as a whole and its various components

• apply engineering principles and data to a design, construction or production activity

Pavement Design Supplement, Transport and Main Roads, July 2018 ii

• take into account local area or project-specific issues, including when the typical assumptions and standards in this supplement are being considered

• optimise initial designs and in-service treatments to suit budget and whole-of-life cost issues.

As this supplement is not a prescriptive standard, reference to it in contract documents will typically also require project-specific requirements appropriate for the contract to be included in a pavement design brief. A pavement design brief is essential for projects where the designer is external to Transport and Main Roads, particularly where the contract is a type where the designer is employed or engaged by a third party such as a construction contractor or developer. A more detailed brief is likely required for these types of contracts, as compared to construct only contracts. Further guidance on developing project design briefs is included in Section 1.2.

Due to differences between design inputs and whole-of-life actualities (e.g. traffic growth, enforcement of and changes to legislation relating to heavy vehicle loading, variability in construction, accuracy of design models, environmental considerations and ongoing maintenance and rehabilitation) the guidance contained in AGPT02 and this supplement can provide only an indication of future pavement performance. Specifically, the guidance provided for typical design assumptions and standards is based on Transport and Main Roads practice and experience to date, and current future directions, including:

• For the Transport and Main Roads controlled road network, historically the pavement design imperative has been for low cost all-weather connections through the adoption of lower initial standards in order to favour maximum length constructed. This has provided an adequate level of service over the whole network within the context of budgetary constraints and the comparatively large geographical area of Queensland with a relatively low population density.

• Reducing high cost maintenance interventions and associated user disruptions on highly trafficked urban roads remains a priority.

• Vehicle load intensities are increasing, causing increased vertical loading and associated increases in horizontal shear loading.

• Expectations about safety requirements, and

• Delivering value for money, including working within the constraints of limited initial budgets.

Alternatives and exceptions to AGPT02 and this supplement’s typical design assumptions and standards may be necessary for the designer’s project-specific engineering design. In making these professional engineering decisions, designers are implicitly evaluating the engineering risks and benefits to the project based on application of the pertinent engineering technology. Professional engineers will recognise that there may be compounding and interconnected risks and/or opportunities when multiple changes to typical values are applied in determining a design solution.

Where innovations are being considered, designers and project managers should refer to Engineering Innovation in the Department of Transport and Main Roads (Transport and Main Roads, 2014).

How to use this document

This document must be read and applied together with (AGPT02). You must have access to AGPT02 to understand what applies to Transport and Main Roads projects.

Pavement Design Supplement, Transport and Main Roads, July 2018 iii

This document:

• sets out how AGPT02 applies to Transport and Main Roads projects

• has precedence over AGPT02 when applied to Transport and Main Roads projects, and

• has the same chapter and section numbering and headings as AGPT02.

The following table summarises the relationship between AGPT02 and this document:

Applicability Meaning

Accepted The AGPT02 section is accepted.

Accepted, with amendments

Part or all of the AGPT02 section has been accepted with additions, deletions or differences.

New There is no equivalent section in AGPT02.

Not accepted The AGPT02 section is not accepted.

Definitions

The following general amended definitions apply when reading AGPT02.

Reference to… Means

Part 2, AGPT02 and this Part

AGPT02, as amended by this document. For example, a reference to “this Part” in AGPT02 means you must refer to AGPT02, and this Pavement Design Supplement.

Pavement Design Supplement, Transport and Main Roads, July 2018 i

Relationship table

Chapter Section Description Applicability

1

Introduction

1.1 Scope of the Guide and this Part Accepted, with amendments

1.2 Project Scope and Background Data Requirements for Design

Accepted

1.2.1 Investigation and Design Proposal Accepted, with amendments

2

Pavement Design Systems

2.1 General Accepted

2.2 Common Pavement Types –

2.2.1 General Accepted, with amendments

2.2.2 Granular Pavements with Sprayed Seal Surfacings


2.2.3 Cemented Granular Bases with Sprayed Seal Surfacings


2.2.4 Granular Pavements with Thin Asphalt Surfacings


2.2.5 Asphalt over Granular Pavements Accepted, with amendments

2.2.6 Flexible Composite, Deep Strength and Full Depth Asphalt Pavements


2.2.7 Concrete Pavements Accepted, with amendments

2.2.8 Asphalt over Heavily Bound (Cemented) Pavements

New

2.2.9 Foamed Bitumen Stabilised Pavements New

2.3 Overview of Pavement Design Systems Accepted

2.3.1 Input Variables Accepted, with amendments

2.3.2 Selecting a Trial Pavement Configuration Accepted

2.3.3 Structural Analysis Accepted

2.3.4 Distress Prediction Accepted

2.3.5 Comparison of Alternative Designs Accepted

2.4 Shoulders with a Lower Structural Standard New

Pavement Design Supplement, Transport and Main Roads, July 2018 ii


3

Construction and Maintenance Considerations

3.1 General Accepted, with amendments

3.2 Extent and Type of Drainage Accepted, with amendments

3.2.1 Purpose and Details of Drainage Measures Accepted

3.2.2 Drainage of Pavement Materials Accepted, with amendments

3.2.3 Use of a Drainage Blanket Accepted, with amendments

3.2.4 Permeable Pavements on Moisture-sensitive Subgrades

Accepted

3.2.5 Full Depth Asphalt Pavements on Moisture-sensitive Subgrades

Accepted

3.2.6 Treatment of Stormwater Run-off Accepted

3.3 Use of Boxed Construction Accepted

3.4 Availability of Equipment Accepted

3.5 Use of Staged Construction Accepted

3.6 Use of Stabilisation Accepted, with amendments

3.7 Pavement Layering Considerations Accepted, with amendments

3.8 Use of Strain Alleviating Membrane Interlayers Accepted, with amendments

3.9 Environmental and Safety Constraints Accepted, with amendments

3.10 Social Considerations Accepted

3.11 Construction under Traffic Accepted, with amendments

3.12 Maintenance Strategy Accepted

3.13 Acceptable Risk Accepted

3.14 Improved Subgrades –

3.14.1 Soft Subgrades Accepted, with amendments

3.14.2 Improved Layers under Bound Layers Accepted, with amendments

3.15 Surfacing Type Accepted

3.15.1 Sprayed Seals Accepted, with amendments

3.15.2 Asphalt or Concrete Surfaces Accepted

3.15.3 Open-graded Asphalt Accepted, with amendments

3.15.4 Surfacings in Tunnels Accepted

3.16 Pavement Widenings Accepted

3.17 Settlement New

3.18 Pavement Jointing Considerations New

3.19 Thickness of Bituminous Seals New

3.20 Temporary Pavements for High Traffic New

Pavement Design Supplement, Transport and Main Roads, July 2018 iii


4

Environment


4.2 Moisture Environment Accepted, with amendments

4.2.1 Equilibrium Moisture Content (EMC) Accepted

4.3 Temperature Environment Accepted, with amendments

5

Subgrade Evaluation


5.2 Measures of Subgrade Support Accepted

5.3 Factors to be Considered in Estimating Subgrade Support


5.3.1 Subgrade Variability Accepted

5.3.2 Performance Risk Accepted

5.3.3 Sequence of Earthworks Construction Accepted

5.3.4 Compaction Moisture Content Used and Field Density Achieved

Accepted

5.3.5 Moisture Changes during Service Life Accepted, with amendments

5.3.6 Pavement Cross-section and Subsurface Drainage

Accepted

5.3.7 Presence of Weak Layers below the Design Subgrade Level

Accepted

5.3.8 Lime-stabilised subgrades Accepted, with amendments

5.4 Methods for Determining Subgrade Design CBR Value Accepted

5.5 Field Determination of Subgrade CBR Accepted

5.5.1 In situ CBR Test Accepted

5.5.2 Cone Penetrometers Accepted

5.5.3 Deflection Testing Accepted

5.6 Laboratory Determination of Subgrade CBR and Elastic Parameters


5.6.1 Determination of Density for Laboratory Testing


5.6.2 Determination of Moisture Conditions for Laboratory Testing


5.7 Adoption of Presumptive CBR Values Accepted, with amendments

5.8 Limiting Subgrade Strain Criterion Accepted

5.9 Subgrades with Design CBR less than 3% New

Pavement Design Supplement, Transport and Main Roads, July 2018 iv


6

Pavement Materials


6.2 Unbound Granular Materials –

6.2.1 Introduction Accepted, with amendments

6.2.2 Factors Influencing Modulus and Poisson’s Ratio

Accepted

6.2.3 Determination of Modulus of Unbound Granular Materials


6.2.4 Permanent Deformation Accepted

6.3 Modified Granular Materials Accepted, with amendments

6.4 Cemented Materials –

6.4.1 Introduction Accepted, with amendments

6.4.2 Factors Affecting Modulus of Cemented Materials

Accepted

6.4.3 Determination of Design Modulus Accepted, with amendments

6.4.4 Determination of Design Flexural Strength Accepted

6.4.5 Factors Affecting the Fatigue Life of Cemented Materials

Accepted

6.4.6 Determining the In-service Fatigue Characteristics from Laboratory Fatigue Measurements

Accepted

6.4.7 Determining the In-service Fatigue Characteristics from Laboratory Measured Flexural Strength and Modulus

Accepted

6.4.8 Determining the In-service Fatigue Characteristics from Presumptive Flexural Strength and Modulus


6.5 Asphalt –

6.5.1 Introduction Accepted

6.5.2 Factors Affecting Modulus of Asphalt Accepted

6.5.3 Definition of Asphalt Design Modulus Accepted

6.5.4 Determination of Design Modulus from Direct Measurement of Flexural Modulus


6.5.5 Determination of Design Modulus from Measurement of ITT Modulus


6.5.6 Design Modulus from Bitumen Properties and Mix Volumetric Properties


6.5.7 Design Modulus from Published Data Accepted, with amendments

6.5.8 Poisson’s Ratio Accepted

Pavement Design Supplement, Transport and Main Roads, July 2018 v


6

6.5.9 Factors Affecting Asphalt Fatigue Life Accepted, with amendments

6.5.10 Fatigue Criteria Accepted with amendments

6.5.11 Means of Determining Asphalt Fatigue Characteristics

Accepted with amendments

6.5.12 Permanent Deformation of Asphalt Accepted, with amendments

6.5.13 Recycled Asphalt New

6.6 Concrete –


6.6.2 Subbase Concrete Accepted

6.6.3 Subbase Concrete for Flexible Pavements Accepted

6.6.4 Base Concrete Accepted, with amendments

6.7 Foamed Bitumen Stabilised Materials New

6.8 Lightly Bound Granular Materials New

7

Design Traffic


7.2 Role of Traffic in Pavement Design Accepted

7.3 Overview of Procedure for Determining Design Traffic

Accepted

7.4 Procedure for Determining Total Heavy Vehicle Axle Groups

–


7.4.2 Selection of Design Period Accepted, with amendments

7.4.3 Identification of Design Lane Accepted

7.4.4 Initial Daily Heavy Vehicles in the Design Lane


7.4.5 Cumulative Number of Heavy Vehicles when Below Capacity


7.4.6 Cumulative Number of Heavy Vehicles Considering Capacity


7.4.7 Cumulative Heavy Vehicle Axle Groups Accepted

7.4.8 Increases in Load Magnitude Accepted

7.5 Estimation of Traffic Load Distribution (TLD) Accepted, with amendments

7.6 Design Traffic for Flexible Pavements –

7.6.1 Damage to Flexible Pavements Accepted

7.6.2 Pavement Damage in Terms of Equivalent Standard Axle Repetitions

Accepted

7.6.3 Design Traffic for Mechanistic-empirical Design Procedure

Accepted

7.7 Design Traffic for Rigid Pavements Accepted

7.8 Example of Design Traffic Calculations Accepted

Pavement Design Supplement, Transport and Main Roads, July 2018 vi


8

Design of Flexible Pavements


8.2 Mechanistic-empirical Procedure Accepted, with amendments

8.2.1 Selection of Trial Pavement Accepted

8.2.2 Procedure for Elastic Characterisation of Selected Subgrade and Lime-stabilised Subgrade Materials


8.2.3 Procedure for Elastic Characterisation of Granular Materials

Accepted

8.2.4 Procedure for Determining Critical Strains for Asphalt, Cemented Material and Lean-mix Concrete

Accepted

8.2.5 Procedure for Determining Allowable Loading for Asphalt, Cemented Material and Lean-mix Concrete


8.2.6 Consideration of Post-cracking Phase in Cemented Material and Lean-mix Concrete

Accepted

8.2.7 Design of Granular Pavements with Thin Bituminous Surfacings

Accepted

8.2.8 Minimum Support Conditions under Lightly Bound, Asphalt, Heavily Bound (Cemented) and Foamed Bitumen Stabilised Pavements

New

8.3 Empirical Design of Granular Pavements with Thin Bituminous Surfacing


8.3.1 Determination of Basic Thickness Accepted, with amendments

9

Design of Rigid Pavements


9.2 Pavement Types –

9.2.1 Base Types Accepted

9.2.2 Subbase Types Accepted, with amendments

9.2.3 Wearing Surface Accepted, with amendments

9.3 Factors used in Thickness Determination –

9.3.1 Strength of Subgrade Accepted, with amendments

9.3.2 Effective Subgrade Strength Accepted

9.3.3 Base Concrete Strength Accepted

9.3.4 Design Traffic Accepted

9.3.5 Concrete Shoulders Accepted

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9

9.3.6 Project Reliability Accepted

9.4 Base Thickness Design –

9.4.1 General Accepted, with amendments

9.4.2 Base Thickness Design Procedure Accepted

9.4.3 Minimum Base Thickness Accepted, with amendments

9.4.4 Example of the Use of the Design Procedure Accepted

9.4.5 Example Design Charts Accepted

9.4.6 Provision of Dowels Accepted

9.4.7 Provision of Tiebars Accepted

9.5 Reinforcement Design Procedures –

9.5.1 General Accepted

9.5.2 Reinforcement in Plain Concrete Pavements Accepted

9.5.3 Reinforcement in Jointed Reinforced Pavements

Accepted

9.5.4 Reinforcement in Continuously Reinforced Concrete Pavements

Accepted

9.6 Base Anchors Accepted

9.7 Joint Types and Design –


9.7.2 Transverse Contraction Joints Accepted

9.7.3 Transverse Construction Joints Accepted

9.7.4 Expansion and Isolation Joints Accepted

9.7.5 Longitudinal Joints Accepted

9.7.6 Joint Design Accepted

10

Economic Comparison of Designs


10.2 Method for Economic Comparison Accepted

10.3 Construction Costs Accepted

10.4 Maintenance Costs Accepted

10.5 Salvage Value Accepted

10.6 Real Discount Rate Accepted

10.7 Analysis Period Accepted, amendments

10.8 Road User Costs Accepted

10.9 Surfacing Service Lives Accepted

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11

Implementation of Design and Collection of Feedback

11.1 Implementation of Design Accepted

11.2 Collection of Feedback –

11.2.1 Need Accepted, with amendments

11.2.2 Benefits Accepted

11.2.3 Current Australian LTPP Program Accepted

11.2.4 Data Collection Accepted

12

Design of Lightly-Trafficked Pavements


12.2 Pavement Design Systems –

12.2.1 Selecting a Trial Pavement Configuration Accepted

12.3 Construction and Maintenance Considerations

Accepted

12.3.1 Extent and Type of Drainage Accepted

12.3.2 Use of Boxed Construction Accepted

12.3.3 Availability of Equipment Accepted

12.3.4 Use of Staged Construction Accepted

12.3.5 Environmental and Safety Constraints Accepted

12.3.6 Social Considerations Accepted

12.3.7 Maintenance Strategy Accepted

12.4 Environment –


12.4.2 Moisture Accepted, with amendments

12.4.3 Temperature Accepted

12.5 Subgrade Evaluation Accepted

12.5.1 Methods for Estimating Subgrade Support Value

Accepted

12.6 Pavement Materials Accepted

12.6.1 Unbound Granular Materials Accepted, with amendments

12.6.2 Cemented Materials Accepted, with amendments

12.6.3 Asphalt Accepted

12.6.4 Concrete Accepted

12.7 Design Traffic Accepted

12.7.1 Procedure for Determining Total Heavy Vehicle Axle Groups

Accepted

12.7.2 Design Traffic for Flexible Pavements Accepted

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12

12.8 Design of Flexible Pavements Accepted

12.8.1 Mechanistic-empirical Procedure Accepted

12.8.2 Empirical Design of Granular Pavements with Thin Bituminous Surfacing

Accepted

12.8.3 Mechanistic-empirical Procedure – Example Charts

Accepted

12.9 Design of Rigid Pavements –


12.9.2 Pavement Types Accepted

12.9.3 Factors Used in Thickness Determination Accepted

12.9.4 Base Thickness Design Accepted

12.9.5 Reinforcement Design Procedures Accepted

12.9.6 Joints Accepted

12.10 Implementation of Design and Collection of Feedback

Accepted

13 References

Appendices

A Australasian Road Agency Pavement Design Manuals or Supplements

Accepted

B Weighted Mean Annual Pavement Temperature Accepted

C Calculating CGF for Non-Constant Annual Growth Rates

Accepted

D Example Determination of Cumulative Number of Heavy Vehicles Considering Capacity

Accepted

E Characteristics of Traffic at Selected WIM Sites Accepted, with amendments

F Adjustment of Design Traffic for Anticipated Increases in Load Magnitude

Accepted

G Traffic Load Distribution Accepted

H Pavement Damage in Terms of Equivalent Standard Axles

Accepted

I Example of Design Traffic Calculations Accepted

J Procedures for Evaluation of Pavement Damage Due to Specialised Vehicles

Accepted

K Effect of Asphalt Thickness on Fatigue Life of Asphalt-Surfaced Pavements

Accepted

L Examples of Use of the Mechanistic-Empirical Procedure for Flexible Pavements

Accepted

M Examples of the use of the Empirical Design Charts for Granular Pavements with Thin Bituminous Surfacings

Accepted

N Examples of Use of the Design Procedure for Rigid Pavements

Accepted

O Traffic Load Distributions for Lightly-Trafficked Roads Accepted

Pavement Design Supplement, Transport and Main Roads, July 2018 x

Contents

About this document ...............................................................................................................................i

How to use this document .....................................................................................................................ii

Definitions ..............................................................................................................................................iii

Relationship table ....................................................................................................................................i

1 Introduction ....................................................................................................................................1

1.1 Scope of the guide and this part ..................................................................................................... 1

1.2 Project scope and background data requirements for design ........................................................ 2 1.2.1 Investigation and design proposal ..................................................................................2

2 Pavement design systems ............................................................................................................2

2.2 Common pavement types ............................................................................................................... 2 2.2.1 General ...........................................................................................................................2 2.2.2 Granular pavements with sprayed seal surfacings ........................................................4 2.2.3 Cemented granular bases with sprayed seal surfacings................................................5 2.2.4 Granular pavements with thin asphalt surfacings ..........................................................5 2.2.5 Asphalt over granular pavements ...................................................................................6 2.2.6 Flexible composite, deep strength and full depth asphalt pavements ...........................7 2.2.7 Concrete pavements ................................................................................................... 10 2.2.8 Asphalt over heavily bound (cemented) pavements ................................................... 11 2.2.9 Foamed bitumen stabilised pavements ....................................................................... 13

2.3 Overview of pavement design systems ........................................................................................ 16

2.3.1 Input variables............................................................................................................................... 16

2.4 Shoulders with a lower structural standard ................................................................................... 16

3 Construction and maintenance considerations ...................................................................... 18

3.1 General ......................................................................................................................................... 18

3.2 Extent and type of drainage .......................................................................................................... 18 3.2.2 Drainage of pavement materials ................................................................................. 20 3.2.3 Use of a drainage blanket ........................................................................................... 20

3.6 Use of stabilisation ........................................................................................................................ 21

3.7 Pavement layering considerations ................................................................................................ 21

3.8 Use of strain alleviating membrane interlayers ............................................................................. 22

3.9 Environmental and safety constraints ........................................................................................... 22

3.11 Construction under traffic .............................................................................................................. 22

3.14 Improved subgrades ..................................................................................................................... 23 3.14.1 Soft subgrades ............................................................................................................ 23 3.14.2 Improved layers under bound layers ........................................................................... 23

3.15 Surfacing type ............................................................................................................................... 25 3.15.1 Sprayed seals .............................................................................................................. 25 3.15.3 Open-graded asphalt ................................................................................................... 26

3.17 Settlement ..................................................................................................................................... 26

3.18 Pavement jointing considerations ................................................................................................. 26

3.19 Thickness of bituminous seals ...................................................................................................... 26

3.20 Temporary pavements for high traffic ........................................................................................... 26

4 Environment ................................................................................................................................ 27

Pavement Design Supplement, Transport and Main Roads, July 2018 xi

4.1 General ......................................................................................................................................... 27

4.2 Moisture environment ................................................................................................................... 28

4.3 Temperature environment ............................................................................................................ 29

5 Subgrade evaluation .................................................................................................................. 30

5.1 General ......................................................................................................................................... 30

5.3 Factors to be considered in estimating subgrade support ............................................................ 30 5.3.5 Moisture changes during service life ........................................................................... 30 5.3.8 Lime-stabilised subgrades ........................................................................................... 34

5.6 Laboratory determination of subgrade CBR and elastic parameters ........................................... 34 5.6.1 Determination of density for laboratory testing ............................................................ 35 5.6.2 Determination of moisture conditions for laboratory testing ........................................ 35

5.7 Adoption of presumptive CBR values ........................................................................................... 36

5.9 Subgrades with design CBR less than 3% ................................................................................... 36

6 Pavement materials .................................................................................................................... 37

6.1 General ......................................................................................................................................... 37

6.2 Unbound granular materials ......................................................................................................... 37 6.2.1 Introduction .................................................................................................................. 37 6.2.3 Determination of modulus of unbound granular materials .......................................... 39

6.3 Modified granular materials .......................................................................................................... 40

6.4 Cemented materials ...................................................................................................................... 40 6.4.1 Introduction .................................................................................................................. 40 6.4.3 Determination of design modulus ................................................................................ 41 6.4.8 Determining the in-service fatigue characteristics from presumptive flexural strength and modulus ................................................................................................................................. 41

6.5 Asphalt .......................................................................................................................................... 41 6.5.4 Determination of design modulus from direct measurement of flexural modulus ....... 41 6.5.5 Determination of design modulus from measurement of ITT modulus ....................... 42 6.5.6 Design modulus from bitumen properties and mix volumetric properties ................... 42 6.5.7 Design modulus from published data .......................................................................... 42 6.5.9 Factors affecting asphalt fatigue life ............................................................................ 44 6.5.10 Fatigue criteria ............................................................................................................. 44 6.5.11 Means of determining asphalt fatigue characteristics ................................................. 44 6.5.12 Permanent deformation of asphalt .............................................................................. 44

6.6 Concrete ....................................................................................................................................... 45 6.6.4 Base concrete .............................................................................................................. 45

6.7 Foamed bitumen stabilised materials ........................................................................................... 45

6.8 Lightly bound granular materials................................................................................................... 46

7 Design traffic ............................................................................................................................... 47

7.4 Procedure for determining total heavy vehicle axle groups .......................................................... 47 7.4.2 Selection of design period ........................................................................................... 47 7.4.4 Initial daily heavy vehicles in the design lane .............................................................. 47 7.4.5 Cumulative number of heavy vehicles when below capacity ...................................... 48 7.4.6 Cumulative number of heavy vehicles considering capacity ....................................... 48

7.5 Estimation of Traffic Load Distribution (TLD) ................................................................................ 49

8 Design of flexible pavements .................................................................................................... 49

8.1 General ......................................................................................................................................... 49

8.2 Mechanistic-empirical procedure .................................................................................................. 49

Pavement Design Supplement, Transport and Main Roads, July 2018 xii

8.2.2 Procedure for elastic characterisation of selected subgrade and lime-stabilised subgrade materials ....................................................................................................................... 49 8.2.5 Procedure for determining allowable loading for asphalt, cemented material and lean-mix concrete .................................................................................................................................. 51 8.2.8 Minimum support conditions under lightly bound, asphalt, heavily bound (cemented) and foamed bitumen stabilised pavements .................................................................................. 51

8.3 Empirical design of granular pavements with thin bituminous surfacing ...................................... 52 8.3.1 Determination of basic thickness ................................................................................. 52

9 Design of rigid pavements ......................................................................................................... 53

9.2 Pavement types ............................................................................................................................ 53 9.2.2 Subbase types ............................................................................................................. 53 9.2.3 Wearing surface .......................................................................................................... 53

9.3 Factors used in thickness determination ...................................................................................... 54 9.3.1 Strength of subgrade ................................................................................................... 54

9.4 Base thickness design .................................................................................................................. 54 9.4.1 General ........................................................................................................................ 54 9.4.3 Minimum base thickness ............................................................................................. 54

10 Economic comparison of designs ............................................................................................ 55

10.1 General ......................................................................................................................................... 55

10.7 Analysis period.............................................................................................................................. 55

11 Implementation of design and collection of feedback ............................................................ 55

11.2 Collection of feedback .................................................................................................................. 55 11.2.1 Need ............................................................................................................................ 55

12 Design of lightly trafficked pavements ..................................................................................... 55

12.4 Environment .................................................................................................................................. 55 12.4.2 Moisture ....................................................................................................................... 55

12.6 Pavement materials ...................................................................................................................... 55 12.6.1 Unbound granular materials ........................................................................................ 55 12.6.2 Cemented materials .................................................................................................... 56

References ........................................................................................................................................... 57

Appendices .......................................................................................................................................... 59

Appendix E Characteristics of traffic at selected WIM sites .............................................................. 59

E.1 Introduction ................................................................................................................................... 59

E.2 Methods for selecting or deriving TLDs for pavement design ...................................................... 59

E.3 Method 1: TLD from WIM site at or near the project location ....................................................... 59

E.4 Method 2: Class-specific TLDs from relevant WIM site combined with project specific classified vehicle count .......................................................................................................................................... 60

E.5 Method 3: Presumptive class-specific TLDs combined with project specific classified vehicle count ...................................................................................................................................................... 60

E.6 Upper limit on WIM loads .............................................................................................................. 61

E.7 Additional notes on Method 1 ....................................................................................................... 61

Pavement Design Supplement, Transport and Main Roads, July 2018 xiii

Tables

Table 2.2.1 – Guide to the selection of pavement types based on traffic (ESA) ..................................... 3

Table 2.2.2 – Typical structure of granular pavement with sprayed seal surfacing (SG and SG(HD)) .. 5

Table 2.2.3 – Typical structure of heavily bound (cemented) base with sprayed seal ........................... 5

Table 2.2.4 – Typical structure of granular pavement with thin asphalt surfacing (AG(B)) ..................... 6

Table 2.2.5 – Typical structure of asphalt over granular pavement (AG(A)) ........................................... 7

Table 2.2.6(a) – Typical structure of flexible composite pavement (FC) for heavy-duty applications ..... 8

Table 2.2.6(b) – Typical structure of deep strength asphalt pavement (DSA) for heavy-duty applications .............................................................................................................................................. 9

Table 2.2.6(c) – Typical structure of full depth asphalt pavement (FDA) for heavy-duty applications .. 10

Table 2.2.7 – Typical structure of concrete pavement for heavy-duty applications .............................. 11

Table 2.2.8(a) – Typical structure of asphalt over heavily bound (cemented) pavement (ASt(A)) ....... 12

Table 2.2.8(b) – Typical structure of asphalt surfacing over heavily bound (cemented) base pavement (ASt(B)) .................................................................................................................................................. 13

Table 2.2.9(a) – Typical structure of asphalt over foamed bitumen stabilised subbase (AFB(A)) ........ 14

Table 2.2.9(b) – Typical structure of asphalt over foamed bitumen stabilised base pavement (AFB(B)) ............................................................................................................................................................... 15

Table 2.2.9(c) – Typical structure of foamed bitumen stabilised pavement with sprayed seal surfacing (SFB) ..................................................................................................................................................... 16

Table 2.3.1 – Typical project reliability levels ........................................................................................ 16

Table 3.14.1 – Typical minimum cover to provide a stable construction platform ................................ 23

Figure 4.1 – Australian climatic zones (www.bom.gov.au) ................................................................... 27

Figure 4.2(a) – Australian seasonal rainfall zones (www.bom.gov.au) ................................................. 28

Figure 4.2(b) – Median annual isohyets for Queensland ...................................................................... 29

Table 5.3.5 – Guide to classification of expansive soils ........................................................................ 31

Figure 5.3.5 – Typical cover thickness over highly and very highly expansive material for flexible pavements (thickness includes the pavement) ..................................................................................... 33

Table 5.6.2 – Guide to moisture conditions for laboratory CBR testing ................................................ 35

Table 5.9 - Minimum thickness of coarse granular or rock fill required for the adoption of a presumptive design CBR of 3% ................................................................................................................................. 37

Table 6.2.1 – Typical application of standard materials in unbound granular pavements with thin bituminous surfacings ............................................................................................................................ 39

Table 6.2.3(a) – Presumptive values for elastic characterisation of unbound granular base materials under thin bituminous surfacings ........................................................................................................... 40

Pavement Design Supplement, Transport and Main Roads, July 2018 xiv

Table 6.2.3(b) – Presumptive values for elastic characterisation of unbound granular materials used as subbase / improved layer under bound pavement layers ..................................................................... 40

Table 6.4.3 – Presumptive values for elastic characterisation of standard heavily bound (cemented) materials ................................................................................................................................................ 41

Table 6.4.8 – Presumptive fatigue constants for standard heavily bound (cemented) materials ......... 41

Table 6.5.7(a) – Presumptive values for elastic characterisation of asphalt mixes at a WMAPT of 32ºC ............................................................................................................................................................... 43

Table 6.5.7(b) – Presumptive heavy vehicle operating speeds ............................................................ 43

Table 6.5.12 – Guide to the selection of dense graded asphalt (AC) mix type and binder class ......... 45

Table 6.7 – Temperature correction factors for determination of foamed bitumen stabilised material design modulus ..................................................................................................................................... 46

Table 6.8 – Presumptive values for elastic characterisation of lightly bound granular materials .......... 47

Table 7.4.2 – Typical design periods ..................................................................................................... 47

Table 7.4.5 – Presumptive growth rates for below capacity traffic flow based on freight forecasts ...... 48

Table E.6 – Upper limit on WIM loads ................................................................................................... 61

Figures

Figure 8.2.2 – Example of revised sublayering for selected subgrade materials .................................. 51

Figure 8.3.1 – Modified design traffic for an increased terminal roughness condition .......................... 53

Figure E.2 – Hierarchy for selecting TLDs ............................................................................................ 59

Supplement to ‘Part 2: Pavement Structural Design’ of the Austroads Guide to Pavement Technology

Pavement Design Supplement, Transport and Main Roads, July 2018 1

1 Introduction

1.1 Scope of the guide and this part

Addition

This supplement is for the design of pavements that are within the scope of AGPT02. Limitations of AGPT02 in terms of its scope also apply to this supplement.

Pavements are assumed to be constructed to Transport and Main Roads quality requirements and standards.

This supplement and AGPT02 are part of a suite of technical documents which are relevant to the design and construction of pavements on Transport and Main Roads projects. Other components of the suite include the Austroads Guide to Pavement Technology (Parts 1 to 10) and the following Transport and Main Roads documents:

• Specifications and Technical Specifications

• Pavement Rehabilitation Manual

• Road Planning and Design Manual

• Materials Testing Manual

• Road Drainage Manual

• Transport Noise Management Code of Practice

• Skid Resistance Management Plan

• Standard Drawings

• Transport Infrastructure Asset Management Policy

• Engineering Notes, Engineering Policies and Technical Notes

• Western Queensland Best Practice Guidelines

• Supplementary Specifications and Test Methods

• Risk Management Framework

• Risk Management Organisational Policy

• Guidelines for Strategic Road Network Planning

This supplement and AGPT02 do not specifically address the selection of pavement surfacings. In some cases, surfacings types have been included to illustrate common design outcomes. For project-specific selection, designers and project managers are referred to:

• Part 3: Pavement Surfacings of the Austroads Guide to Pavement Technology (Austroads, 2009a), and

• Transport and Main Roads Technical Note TN175 Selection and Design of Sprayed Bituminous Treatments.



1.2 Project scope and background data requirements for design

1.2.1 Investigation and design proposal

Addition

For Transport and Main Roads projects, the proposal (often referred to as the pavement design brief) details the required outcomes of pavement design including:

• assumptions regarding design inputs and level of acceptable risk

• project scope requirements listed in Table 1.1 of AGPT02, and

• method of reporting alternatives and exceptions (such as departures from the “typical” assumptions, methodology and standards in AGPT02 and this supplement) for Transport and Main Roads approval / acceptance, including:

i. reasons for the departure

ii. technical justification with supporting evidence

iii. requirements for implementation (for example, modifications and/or additions to technical specifications)

iv. estimated cost savings or additional costs, and

v. anticipated and/or potential impacts, including those on road users, serviceability, durability, whole-of-life performance, construction program, functional performance, maintenance requirements and safety.

Designers are expected to seek prompt clarification from Transport and Main Roads regarding any aspects of the design requirements that are unclear or missing from the design brief.

2 Pavement design systems

2.2 Common pavement types

2.2.1 General

Addition

The choice of pavement type requires consideration of project-specific factors which may include:

• horizontal shear stresses on grades, curves and intersections (for example, granular pavements with sprayed seal surfacing may not be suitable in some locations; and, for granular pavements with thin asphalt surfacings, it may be necessary to increase the thickness of asphalt in these areas)

• likely in-service moisture conditions may limit the suitability of unbound granular materials

• heavy vehicle loads and/or pavement contact stresses higher than those used in the development of the current pavement design models and technical specifications

• availability and adequacy of materials and costs of transporting materials

• adoption of standards higher than the minimums in the technical specifications (for example, when the standard of available materials is well in excess of the technical specifications) may reduce the performance risk for some pavement types

• availability and adequacy of construction equipment and expertise



• construction constraints (for example, construction under traffic may preclude the adoption of pavement materials that require long curing periods prior to trafficking)

• changes to the road network and/or function / classification of the road during the design period

• land development

• specific functional requirements (for example, safety, noise)

• current and future traffic characteristics including anticipated changes to vehicle mass limits and tyre pressures during the design period

• subgrade settlement and/or water-induced volume change which may impact on pavements with heavily bound (cemented) or rigid layers

• whole-of-life costs which may include both direct and indirect costs such as structural interventions, maintenance, rehabilitation, modifying drainage structures, increasing clearances, modifying safety barriers, providing temporary access, maintaining alternative routes, delays and disruptions to road users

• sustainability requirements such as local laws, policies and regulations

• current and future budget considerations, and

• local environmental conditions.

A guide to the selection of pavement types for Transport and Main Roads projects based on traffic loading is provided in Table 2.2.1. This guide is intended to be used in conjunction with local practice and experience, and with the consideration of project-specific factors.

Table 2.2.1 – Guide to the selection of pavement types based on traffic (ESA)

Pavement Type

Rural Urban

Average Daily ESA in Design Lane in Year of Opening

< 10

0

100

to

< 50

0

500

to

< 10

00

1000

to

< 30

00

≥ 30

00

< 10

0

100

to

< 50

0

500

to

< 10

00

1000

to

< 30

00

≥ 30

00

SG # # #

SG(HD) #

LBB

SFB # # #

AG(B) * * * *

AFB(B)

AG(A)

ASt(A)

ASt(B)

FC

DSA

AFB(A)



Pavement Type

Rural Urban

Average Daily ESA in Design Lane in Year of Opening

< 10

0

100

to

< 50

0

500

to

< 10

00

1000

to

< 30

00

≥ 30

00

< 10

0

100

to

< 50

0

500

to

< 10

00

1000

to

< 30

00

≥ 30

00

FDA

Rigid

Notes and Abbreviations

Typically suitable

* Typically suitable where the asphalt fatigue life is acceptable

# Typically suitable where a sprayed seal surfacing is acceptable

May be suitable following project-specific assessment (for example, to consider relatively high initial cost and/or performance risk)

Not typically adopted due to relatively high initial cost

Typically unsuitable due to anticipated poor or uncertain performance

SG Unbound granular pavement with sprayed seal surfacing (Table 2.2.2)

SG(HD) Heavy duty unbound granular pavement with sprayed seal surfacing (Table 2.2.2)

LBB Lightly bound granular base with sprayed seal or asphalt surfacing (refer to Section 6.8)

SFB Foamed bitumen stabilised pavement with sprayed seal surfacing (Table 2.2.9(c))

AG(B) Unbound granular pavement with thin asphalt surfacing (Table 2.2.4)

AFB(B) Asphalt over foamed bitumen stabilised base pavement (Table 2.2.9(b))

AG(A) Asphalt over granular pavement (Table 2.2.5)

ASt(a) Asphalt over heavily bound (cemented) pavement (Table 2.2.8(a))

ASt(B) Heavily bound (cemented) base with thin asphalt surfacing (Table 2.2.8(b))

FC Flexible composite pavement (Table 2.2.6(a))

DSA Deep strength asphalt pavement (Table 2.2.6(b))

AFB(A) Asphalt over foamed bitumen stabilised subbase pavement (Table 2.2.9(a))

FDA Full depth asphalt pavement (Table 2.2.6(c))

Rigid Concrete pavement (Table 2.2.7)

2.2.2 Granular pavements with sprayed seal surfacings

Addition

The typical structure of a granular pavement with a sprayed seal surfacing (SG and SG(HD)) is as shown in Table 2.2.2.



Table 2.2.2 – Typical structure of granular pavement with sprayed seal surfacing (SG and SG(HD))

Course Description (typical)

Surfacing1 Prime plus sprayed seal

Base and subbase

Unbound granular or recycled material blend selected using Table 6.2.1. Thicknesses are typically determined from Figure 8.4 of AGPT02 or Figure 12.2 of AGPT02. Further guidance on SG(HD) pavements is provided in Transport and Main Roads Technical Note TN171 Use of High Standard Granular (HSG) Bases in Heavy Duty Unbound Granular Pavements.

Notes:

1. Refer to Transport and Main Roads Technical Note TN175 Selection and Design of Sprayed Bituminous Treatments for further guidance.

2.2.3 Cemented granular bases with sprayed seal surfacings

Addition

Pavements comprised of a heavily bound (cemented) granular base with sprayed seal surfacing are at times adopted by Transport and Main Roads for floodways in remote areas where more resilient concrete pavements are determined to be uneconomical on a whole-of-life basis. The typical structure of such a pavement is as shown in Table 2.2.3. Due to the significant maintenance / performance issues associated with this pavement type, it should only be adopted after a rigorous pavement selection process has been undertaken that compares it to other alternatives.

Table 2.2.3 – Typical structure of heavily bound (cemented) base with sprayed seal


Surfacing1,2 Prime plus sprayed seal

Base Minimum 150 mm Cat 1 or Cat 2 heavily bound (cemented) material (thickness determined by mechanistic-empirical design)

Subbase If required, minimum 150 mm Type 2.3 unbound granular material or RM003 recycled material blend, or lightly bound improved layer (refer to Section 3.14.2 for further details).

Notes:

1. Where improved resistance to reflective cracking is required, a strain alleviating membrane (SAM-S or SAM-R) or a geotextile seal (GRS-S/S or GRS-D/D) should be considered. In locations susceptible to flooding, additional measures to reduce the risk of geotextile separation from the pavement should be implemented as detailed in the Transport and Main Roads Pavement Rehabilitation Manual.


2.2.4 Granular pavements with thin asphalt surfacings

Addition

The typical structure of a granular pavement with thin asphalt surfacing (AG(B)) is as shown in Table 2.2.4.



Table 2.2.4 – Typical structure of granular pavement with thin asphalt surfacing (AG(B))


Surfacing1 AC10M³, AC10H³, AC14M², AC14H², SMA10 or SMA14² OG10 or OG14

Seal4 N/A 10 or 14 mm waterproofing seal under asphalt (WP-A)

Intermediate N/A AC10M², AC10H², AC14M² or AC14H²

Prime and seal Prime plus 10 or 14 mm nominal size C170 S/S seal

Base and subbase

Unbound granular or recycled material blend selected using Table 6.2.1. Thicknesses are typically determined from Figure 8.4 of AGPT02, Figure 12.2 of AGPT02 or mechanistic-empirical design.

Notes:

1. Refer to Table 6.5.12 for guidance on the selection of dense graded asphalt mix type and binder class.

2. The fatigue life of the asphalt should be assessed using mechanistic-empirical design.

3. Refer to Section 8.2.7 of AGPT02 for guidance on the design of asphalt surfacings less than 40 mm thick. AC10M and AC10H are typically limited to locations with design traffic less than 100 ESA/day at opening when C320 binder is used and 300 ESA/day at opening when A15E binder is used.


2.2.5 Asphalt over granular pavements

Addition

The typical structure of an asphalt over granular pavement (AG(A)) is as shown in Table 2.2.5.



Table 2.2.5 – Typical structure of asphalt over granular pavement (AG(A))


Surfacing1 AC14M, AC14H, SMA10 or SMA14 OG10 or OG14

Seal² N/A³ 10 or 14 mm waterproofing seal under asphalt (WP-A)

Intermediate1 N/A AC14M or AC14H

Base1 AC14M, AC14H, AC20M, AC20H or EME2 with thickness determined by mechanistic-empirical design

Prime and seal4 Prime plus 10 or 14 mm nominal size C170 S/S seal

Subbase (improved layer)

Minimum 150 mm Type 2.3 unbound granular material or RM003 recycled material blend, or lightly bound improved layer. Where the traffic in the design lane at opening is 1000 ESA/day or more, minimum support conditions also apply. Refer to Sections 3.14.2 and 8.2.8 for further details.

Notes:

1. Refer to Table 6.5.12 for further guidance on the selection of dense graded asphalt mix type and binder class.


3. The waterproofing seal under dense graded asphalt and stone mastic asphalt is typically omitted where the asphalt contractor has demonstrated a history of conformance with the insitu air voids requirements. Refer to Section 3.7 for details.

4. Refer to Section 3.14.2 for further guidance on priming and sealing the improved layer/subbase.

2.2.6 Flexible composite, deep strength and full depth asphalt pavements

Addition

Typical structures of flexible composite (FC), deep strength asphalt (DSA) and full depth asphalt (FDA) pavements used in heavy-duty applications are as shown in Tables 2.2.6(a), 2.2.6(b) and 2.2.6(c).

Transport and Main Roads has limited experience with the use of flexible composite pavements.

Cracking of heavily bound (cemented) materials, and subsequent reflection into overlying asphalt layers, should be anticipated in deep strength asphalt pavements.



Table 2.2.6(a) – Typical structure of flexible composite pavement (FC) for heavy-duty applications


Surfacing1 AC14M, AC14H, SMA10 or SMA14

OG10 or OG14


Intermediate1 AC14M or AC14H

Base1 AC20M or AC20H with thickness determined by mechanistic-empirical design and to provide at least 175 mm of asphalt (excluding open graded asphalt) in the total pavement structure.

Curing compound and seal Bitumen emulsion plus a SAMI seal3,4

Subbase 150 to 230 mm lean-mix concrete


Improved layer Minimum 150 mm lightly bound improved layer. Where the traffic in the design lane at opening is 1000 ESA/day or more, minimum support conditions also apply. Refer to Sections 3.14.2 and 8.2.8 for further details.

Notes:




4. The SAMI seal can be substituted with a 7 mm C170 S/S seal where an increased risk of future reflective cracking is accepted by the Transport and Main Roads project representative.

5. Refer to Section 3.14.2 for further guidance on priming and sealing the improved layer.



Table 2.2.6(b) – Typical structure of deep strength asphalt pavement (DSA) for heavy-duty applications



OG10 or OG14



Base1 AC20M or AC20H with thickness determined by mechanistic-empirical design and to provide at least 175 mm of asphalt (excluding open graded asphalt) in the total pavement structure.

Prime and seal Prime plus a SAMI seal³

Subbase 150 to 200 mm Cat 1 or Cat 2 heavily bound (cemented) material



Notes:







Table 2.2.6(c) – Typical structure of full depth asphalt pavement (FDA) for heavy-duty applications



OG10 or OG14



Base1 AC20M, AC20H or EME2 with thickness determined by mechanistic-empirical design



Notes:





2.2.7 Concrete pavements

Addition

The typical structure of concrete pavement used in heavy-duty applications is as shown in Table 2.2.7.



Table 2.2.7 – Typical structure of concrete pavement for heavy-duty applications


Base1,2 Jointed and unreinforced Plain Concrete Pavement (PCP) Jointed Reinforced Concrete Pavement (JRCP) Continuously Reinforced Concrete Pavement (CRCP), or Steel Fibre reinforced Concrete Pavement (SFCP)

Curing and debonding Curing and debonding treatment

Subbase Minimum 150 mm lean-mix concrete



Notes:

1. The base course typically also functions as the pavement surfacing if it meets surface property requirements. However, in some cases an additional asphalt surfacing is provided over CRCP (refer to Section 9.2.3).

2. Diamond grinding may be required to meet surface property requirements.


2.2.8 Asphalt over heavily bound (cemented) pavements

New

There are two general design approaches typically adopted for asphalt over heavily bound (cemented) pavements. These are:

a) Asphalt base over heavily bound (cemented) subbase (ASt(A)) – this pavement type comprises an asphalt surfacing, asphalt intermediate course (where relevant) and asphalt base, as shown in Table 2.2.8(a). A minimum of 175 mm of asphalt (excluding open graded asphalt) and a SAMI are typically provided to inhibit cracks in the subbase reflecting through the asphalt. However, even with these provisions, cracking of the heavily bound (cemented) material and subsequent reflection into overlying asphalt layers should be anticipated.

b) Asphalt surfacing over heavily bound (cemented) base (ASt(B)) – this pavement type comprises an asphalt surfacing and asphalt intermediate course (where relevant) over a heavily bound (cemented) base, as shown in Table 2.2.8(b). The total asphalt thickness (excluding open graded asphalt) is typically less than 175 mm, meaning reflection of cracks through the asphalt should be expected relatively early in the life of the pavement. This pavement type carries similar performance risks as the heavily bound (cemented) granular base with sprayed seal surfacing pavement type detailed in Section 2.2.3. This pavement type is typically only adopted for temporary pavements or where the need for future maintenance interventions has been carefully considered and accepted.



Table 2.2.8(a) – Typical structure of asphalt over heavily bound (cemented) pavement (ASt(A))



OG10 or OG14

Sea² N/A³ 10 or 14 mm waterproofing seal under asphalt (WP-A)

Intermediate1 N/A AC14M or AC14H

Base1 AC14M, AC14H, AC20M or AC20H with thickness determined by mechanistic-empirical design and to provide at least 175 mm of asphalt (excluding open graded asphalt) in the total pavement structure.

Prime and seal Prime plus a SAMI seal3,4

Subbase 150 to 200 mm Cat 1 or Cat 2 heavily bound (cemented) material


Improved layer Minimum 150 mm Type 2.3 unbound granular material or RM003 recycled material blend, or lightly bound improved layer. Where the traffic in the design lane at opening is 1000 ESA/day or more, minimum support conditions also apply. Refer to Sections 3.14.2 and 8.2.8 for further details.

Notes:




4. As an alternative to a SAMI seal, a geotextile reinforced sprayed seal (GRS-S/S) may be provided to further inhibit crack reflection.




Table 2.2.8(b) – Typical structure of asphalt surfacing over heavily bound (cemented) base pavement (ASt(B))


Surfacing1,2,3 AC14M, AC14H, SMA10 or SMA14

OG10 or OG14

Intermediate1,3 AC14M or AC14H (if required) AC14M or AC14H

Prime and seal Prime plus a SAMI seal4,5

Base6 Heavily bound (cemented) material typically specified with an appropriate project-specific technical specification with provisions to reduce the risk of cracking. The thickness of the base is determined by mechanistic-empirical design.


Improved layer 150 to 300 mm unbound granular material or lightly bound improved layer, or an appropriate selected fill material (refer to Section 3.14.2 for further details).

Notes:

1. Refer to Table 6.5.12 for guidance on the selection of dense graded asphalt mix type and binder class.

2. Refer to Section 3.7 for guidance on the use of waterproofing seals.

3. The total thickness of asphalt (excluding open graded asphalt) is typically 100 mm for design traffic between 1000 and 3000 ESA/day in the design lane in the year of opening, and 50 mm for traffic less than 1000 ESA/day in the design lane in the year of opening.

4. As an alternative to a SAMI seal, a geotextile reinforced sprayed seal (GRS-S/S) may be provided to further inhibit crack reflection.

5. At locations subject to significant horizontal loads (as detailed in Section 8.2.7 of AGPT02), it may be necessary to adopt an alternative treatment to enhance bonding and/or increase the overlying asphalt thickness to reduce the risk of shearing at the SAMI/GRS layer interface.

6. For temporary pavements, the base typically comprises a minimum 150 mm Cat 1 or Cat 2 heavily bound (cemented) material (thickness determined by mechanistic-empirical design).


2.2.9 Foamed bitumen stabilised pavements

New

Foamed bitumen stabilised pavements include the following general types:

a) Asphalt over foamed bitumen stabilised subbase (AFB(A)). This pavement type comprises asphalt surfacing, intermediate and base courses over foamed bitumen stabilised granular material in the subbase (upper and lower), as shown in Table 2.2.9(a).

b) Asphalt over foamed bitumen stabilised base (AFB(B)). This pavement type comprises asphalt surfacing and an asphalt intermediate course (where required) over foamed bitumen stabilised granular material in the base and subbase, as shown in Table 2.2.9(b).

c) Foamed bitumen stabilised pavement with sprayed seal surfacing (SFB). This pavement type comprises sprayed seal surfacing over foamed bitumen stabilised granular material in the base and subbase, as shown in Table 2.2.9(c).



Table 2.2.9(a) – Typical structure of asphalt over foamed bitumen stabilised subbase (AFB(A))



OG10 or OG14



Base1 AC20M, AC20H or EME2

Seal² 7 or 10 mm nominal size with C170, or bituminous emulsion

Subbase4 Minimum 300 mm foamed bitumen stabilised granular material with thickness determined by mechanistic-empirical design

Improved layer5,6 Minimum 100 mm unbound granular or fill material. Minimum support conditions also apply. Refer to Sections 3.14.2 and 8.2.8 for further details. Cementitious materials must not be used.

Notes:




4. Minimum total thickness of 300 mm requires plant-mixed foamed bitumen stabilised granular material to be constructed in multiple layers, with each constructed layer between 125 and 250 mm thick. A 7 or 10 mm nominal size seal (with C170, or bituminous emulsion) between successive plant-mixed foamed bitumen stabilised granular layers may be required. Refer to Section 3.14.2 for guidance on sealing between foamed bitumen stabilised granular layers.

5. The improved layer is typically omitted where the subgrade design CBR ≥ 7%.

6. Where the expansive nature of the subgrade is very high (as defined in Table 5.2 of AGPT02), a subgrade geo-composite layer (MRTS58 Subgrade Reinforcement using Pavement Geosynthetics) is typically provided at subgrade level (in addition to any other treatments determined from Figure 5.3.5 and/or recommended in the geotechnical assessment detailed in Section 5.3.5).



Table 2.2.9(b) – Typical structure of asphalt over foamed bitumen stabilised base pavement (AFB(B))


Surfacing1 AC10M, AC10H, AC14M, AC14H, SMA10 or SMA14

OG10 or OG14


Intermediate4 AC10M, AC10H, AC14M or AC14H (if required)

AC10M, AC10H, AC14M or AC14H

Seal² 7 or 10 mm nominal size with C170, or bituminous emulsion

Base5 Minimum 300 mm foamed bitumen stabilised granular material with thickness determined by mechanistic-empirical design


Notes:




4. Where the surfacing is dense graded or stone mastic asphalt, the intermediate course is typically omitted where the average daily traffic in the design lane in the year of opening is less than 500 ESA.






Table 2.2.9(c) – Typical structure of foamed bitumen stabilised pavement with sprayed seal surfacing (SFB)


Surfacing1 Sprayed seal

Seal1 7 or 10 mm nominal size with C170, or bituminous emulsion

Base² Minimum 300 mm foamed bitumen stabilised granular material with thickness determined by mechanistic-empirical design


Notes:





2.3 Overview of pavement design systems

2.3.1 Input variables

Addition

Project reliability

The project reliability levels typically adopted by Transport and Main Roads are listed in Table 2.3.1.

Table 2.3.1 – Typical project reliability levels

Road Category Typical Project Reliability Levels (%)

Freeways (Motorways) (includes connections between motorways)

95

All other roads (includes motorway ramps, highways and main roads)

90

2.4 Shoulders with a lower structural standard

New

There are two broad design alternatives for shoulders:

1. Continue all layers of the pavement for the adjacent trafficked lane across the shoulder. This approach is typically adopted as it is generally more practical to construct with a lower risk of construction variability, and/or lower risk of moisture issues.



2. Design and construct the shoulder to a lower structural standard than the adjacent trafficked lane to reduce the initial pavement capital cost.

In both cases, the pavement in the trafficked lane should extend at least 200 mm beyond the delineated edge of the trafficked lane for heavy-duty pavements, and at least 100 mm for other pavements. In some instances it may be beneficial to extend the pavement for the trafficked lane a greater distance into the shoulder to facilitate future widening (for example, to accommodate portable concrete barriers and/or lane realignments).

A lower standard shoulder is not typically used on the high side of pavements as this could result in moisture entering the pavement.

Where a shoulder of a structural standard lower than that of the adjacent trafficked lane of the pavement is adopted, the following should be provided:

• The total pavement thickness of the shoulder should be the same as the adjacent trafficked lane.

• Where the adjacent trafficked lane of the pavement is asphalt over granular, full depth asphalt, deep strength asphalt, flexible composite, or similar, the shoulder should have the same asphalt surfacing, seal and intermediate courses / layers as the adjacent trafficked lane. Beneath this, the thickness of asphalt or sealed unbound granular base, should be designed to ensure that the asphalt has acceptable fatigue life. The balance of material down to the top of the granular subbase or improved layer would then typically be a granular subbase material. A pavement drain is included at the interface of the shoulder pavement and the adjacent trafficked lane pavement.

• Where the adjacent trafficked lane of the pavement is a granular pavement with a sprayed seal or thin asphalt surfacing, the shoulder should have the same asphalt layers and seal as the adjacent trafficked pavement. The shoulder should also have the same granular base layer(s) and materials as the adjacent trafficked pavement. The balance of the thickness of the shoulder to the level of the lowest pavement layer can be a select fill material. General fill may not be appropriate if its permeability is low relative to the adjacent trafficked pavement, as this may inhibit drainage of the pavement layers.

• Where the adjacent trafficked lane of the pavement is concrete, a minimum asphalt thickness of 50 mm is typically provided in the shoulder. Where the adjacent concrete pavement also includes an asphalt surfacing, all bituminous layers (such as the surfacing, seal and intermediate course) are typically also included in the shoulder. Beneath this, the thickness of asphalt or sealed unbound granular base should be designed to ensure that the asphalt has acceptable fatigue life. The balance of material down to the top of the improved layer would then typically be a granular subbase material. A concrete edge drain is included at the interface of the two pavements.

• In all cases, it is typical practice to continue the seal to the outside edge of any verge, or if a verge does not exist, to the outside edge of the shoulder.

Where a shoulder of a structural standard lower than that of the trafficked lanes is constructed as a widening to an existing pavement, the effect of excavating into the insitu subgrade materials should be considered in determining the thickness of the shoulder (for example, consider the risks of exposing low strength materials).



There are some limitations to the use of shoulders of a structural standard lower than that of the trafficked lanes. These limitations include applications where:

• construction may be more difficult because of increased complexity and narrow working widths

• future widening may be more difficult

• with concrete pavements, a thicker base course is typically required for trafficked lanes

• temporary trafficking of the shoulder during construction and future maintenance of the through lanes may be restricted, and/or

• some shoulders may experience regular trafficking because of the nature of the road alignment (for example, curves, end of tapers, narrow through lanes, access points, intersections and/or no edge lines).

3 Construction and maintenance considerations

3.1 General

Addition

It is assumed that Transport and Main Roads standards for construction and maintenance will be adopted.

3.2 Extent and type of drainage

Addition

In addition to the drainage provisions discussed in Part 10: Subsurface Drainage of the Austroads Guide to Pavement Technology (Austroads, 2009b), the following cross-sectional provisions should be considered to reduce the exposure of the pavement and subgrade materials to moisture infiltration:

1. Seal over the full width of the formation (traffic lanes and shoulders).

2. On the high side of one-way cross-falls:

a. seal the shoulder and verge, and maintain the seal in a sound condition, and/or

b. provide appropriate subsoil drainage to intercept water seepage before it reaches the pavement or subgrade.

3. In cuttings:

a. provide table drains where an unbound granular pavement is used

b. provide table drains or subsurface pavement drains where a bound or rigid pavement is used, and

c. where rock floors are present, use a heavily bound (cemented) infill, or dental concrete, with surface cross-fall so that water ponding does not occur.

4. In wet regions, the formation should be kept as high as economically possible over flat terrain so as to improve moisture contents.

5. Maximise cross-fall within the permissible range for geometric design.

6. Design divided roads with two-way cross-fall (where possible).



7. Longitudinal drainage, such as table drains (where used), should be:

a. located away from the formation (typically minimum 5 m) in flat or lightly undulating country or excluded altogether

b. directed away from the formation

c. appropriately shaped (refer to the Transport and Main Roads Road Drainage Manual), and

d. such that the invert level is lower than subgrade level in cuttings, to intercept seepage before it reaches the pavement or subgrade. Typically the invert is located at least 200 mm below the top of subgrade (or bottom of a drainage blanket, where present).

8. Compact pavement materials right up to the edge of the pavement to the specified compaction standard, and remove any excess, poorly compacted paving material beyond the seal edges.

9. In drier areas (that is, arid and semi-arid areas), particularly if design traffic volumes are less than 106 ESAs, low permeability paving materials may have benefits in relation to reducing moisture infiltration into the subgrade. However, such materials may have lower strength than standard materials so their suitability should be considered on a case-by-case basis.

10. In situations where the shoulder is narrow and the verge is not sealed, the runoff flow path may be hindered (for example, by a grassed verge) resulting in moisture entry into the pavement over time. In such situations, consideration should be given to the likely impact on the pavement, in particular unbound pavements.

11. Pavement drains (MRTS38 Pavement Drains) at interfaces between pavements comprising different structures and/or materials.

Moisture from seepage, infiltration through the surfacing and from water table fluctuations, can be controlled by the installation of properly designed pavement and subgrade drains. However, drains are only effective when subgrade moisture is subject to hydrostatic head (positive pore pressures). It is common for fine grained subgrade materials (silts and clays) to have equilibrium moisture contents above optimum moisture content, yet, because pore pressures are not positive, they cannot be drained. While subsurface drainage does play an important role in moisture control, unrealistic assumptions about the effect of subsurface drainage on subgrade moisture condition should not be made.

In some circumstances, subsurface drainage or other types of drainage may need to be constructed well before the pavement to help drain wet subgrades and aid in pavement construction.

The time required to drain a wet subgrade will depend on the permeability of the subgrade material, type and spacing of drains and the extent of additional water in flows. If it is not possible to provide subgrade drainage, or an adequate drainage time, the design should allow for wet conditions, and material types and construction methods should be selected accordingly.

Where pavement or subgrade drainage measures are proposed, the construction sequence should ensure that drainage is installed early enough to prevent a build-up of water in the pavement and/or subgrade due to rain during construction.

Consideration should be given to the construction sequence to ensure that drainage installations are not rendered ineffective, even temporarily, by later construction activities. Careful planning in this area



can minimise delays to construction caused by wet weather as well as ensure that future pavement performance is not compromised.

Maintenance of drainage provisions is essential, particularly for unbound granular pavements. This may include routine checking and flushing of subsoil drains, and cleaning of surface drains.

3.2.2 Drainage of pavement materials

Addition

Cemented materials can be quite permeable and water has been found to travel long distances within a layer of cemented material. In addition, shrinkage cracks within these materials can become avenues of rapid moisture movement. Boundaries between layers inadequately bonded together have also been found to allow rapid water movements.

The results of accelerated loading tests (NAASRA, 1987a) as well as observations of field performance have shown that rapid water movement in cemented layers can cause erosion, weakening and subsequent failure of these layers. Thus, if cemented materials are proposed in the pavement structure, consideration should be given to providing effective drainage for these layers.

3.2.3 Use of a drainage blanket

Addition

An alternative to an open-graded 20 mm crushed rock is a larger size (typically 125 mm nominal size and 300 mm thick) rock fill. Rock fill is particularly suited to locations with soft subgrades, or where a high drainage capacity is required. The rock fill is typically wrapped in a suitable geotextile (MRTS27 Geotextiles (Separation and Filtration)) and covered by a 150 mm thick heavily bound (cemented) material or lightly bound improved layer to provide a stable platform for pavement construction.

For the purpose of pavement thickness design, crushed rock and rock fill drainage blankets are typically modelled as selected subgrade material with presumptive vertical modulus limited to a maximum of 150 MPa.

It is important that the material and cross-section is designed to be free draining throughout the service life of the pavement, taking into consideration issues which may impact on future pavement performance including:

• potential for moisture ingress (for example, from inundation) and ability for moisture to drain freely from the material

• maintenance activities that may impact on drainage (for example, inhibiting drainage as a result of grading of drains, shoulders and batters)

• heavy vegetation growth and associated maintenance

• shrink / swell potential of the underlying subgrade material, and

• suction potential of the overlying materials.



3.6 Use of stabilisation

Addition

Guidance on the design of pavements with lime-stabilised subgrades is provided in Transport and Main Roads Technical Note TN74 Structural Design Procedure of Pavements on Lime Stabilised Subgrades.

Use of multi-layer construction for heavily bound (cemented) material courses is not typically adopted when the design traffic is 1000 ESA/day or more at opening due to the performance risk associated with these layers not remaining fully bonded throughout the pavement’s life (even when bonding treatments are used).

Accelerated loading tests at Beerburrum (NAASRA, 1987a) clearly illustrated the consequences of inadequate bonding between layers. Measures to improve the bond between layers are detailed in the relevant technical specifications. The report Cement Slurry Applications to CTB Layer Bonding (Main Roads, 1988) describes the use of these measures in more detail.

Where multi-layer construction is adopted, only the bottom layer may be constructed insitu. Additionally, the first layer should be kept as thick as possible (at least 150 mm) in order to avoid damage to the lower layer by construction traffic placing subsequent layers.

3.7 Pavement layering considerations

Addition

To achieve adequate bonding of asphalt to the underlying layer, preparative treatment including, but not limited to, texturing the underlying surface and/or use of a proprietary bond coat may be required at locations:

a) subject to high shear stresses (for example, from heavy braking and/or tight cornering), such as intersections, roundabouts and approaches, and/or

b) where the surface of a lower asphalt layer is trafficked prior to construction of the overlying layer.

In pavements with multiple asphalt layers, and where the surfacing is open graded asphalt, a waterproofing seal (WP-A) between the asphalt surfacing and the intermediate layer is typically provided.

In pavements with multiple asphalt layers, and where the surfacing is dense graded asphalt or stone mastic asphalt, a 10 or 14 mm waterproofing seal (WP-A) between the asphalt surfacing and the underlying asphalt should be provided as a provisional (if ordered) item. The waterproofing seal should be incorporated into the works until such time that the asphalt contractor has demonstrated a history of compliance with the insitu air voids requirements in MRTS30 Asphalt Pavements for the specific asphalt mixes used. After which time, the layer may be omitted from the works pending ongoing conformance with the air voids requirements of MRTS30 Asphalt Pavements.

On Contracts where a schedule of rates is not adopted, the same principle should apply, with the waterproofing seal being incorporated into the works until such time that the Contractor has demonstrated a history or compliance with the air voids requirements of MRTS30 Asphalt Pavements.

The guidance in the preceding paragraphs should be included in Annexure MRTS30.1 Asphalt Pavements and also be noted on the design drawings.



Asphalt pavements should be designed to minimise the potential for AC20M and AC20H layers to be exposed to wet weather for prolonged periods during construction. Where the construction program dictates that exposure of such layers to wet weather cannot be avoided, an AC14M or AC14H mix should be used for the exposed layer to minimise the potential for moisture ingress and subsequent stripping of the asphalt.

3.8 Use of strain alleviating membrane interlayers

Addition

SAMI seals are typically applied to the surface of heavily bound (cemented) layers to inhibit crack reflection into overlying pavement layers.

3.9 Environmental and safety constraints

Addition

Unbound granular pavements are particularly susceptible to damage caused by the infiltration of water during construction, such as from ponded water, seepage and inundation.

Austroads (2003) provides guidance on the control of moisture in pavements during construction. These factors should be considered during:

• selection of pavement type

• design of the pavement structure (including cross-sectional details)

• programming of works and development of construction methodology, and

• development of contract provisions for the work.

Typically, construction of unbound granular layers includes provisions such that:

• the construction program minimises the potential for exposure of the pavement to rainfall events and/or inundation (for example, sealing the pavement as soon as possible)

• the construction program makes allowance for drying out of pavement layer(s) to below the material’s degree of saturation limit, and

• the options, responsibility and liability for any rectification / rework caused by water infiltration and/or inundation during pavement construction is clearly established in the construction contract.

For concrete pavements, the time from commencement of base paving to completion of base paving to the full carriageway width is typically limited to one month, to minimise any problems relating to differential movements. Likewise, for flexible composite pavements the lean-mix concrete subbase is typically covered within one month to assist in limiting the width of shrinkage cracks.

3.11 Construction under traffic

Addition

Pavement damage, resulting from temporarily trafficking pavement layers below the final surfacing (including excessive construction traffic), should be included in the pavement design calculations. This may include fatigue damage to asphalt, foamed bitumen stabilised and heavily bound (cemented) layers.



3.14 Improved subgrades

3.14.1 Soft subgrades

Addition

This section applies to soft subgrade treatments used to provide a stable construction platform (when the insitu CBR of the subgrade at the time of construction is less than 3%). This is distinguished from when the design subgrade CBR is less than 3% (at the design moisture and density conditions), which is addressed in Section 5.9.

The selection and design of soft subgrade treatment measures necessitates consideration of project-specific factors including expected construction traffic and the subgrade strength at the time of construction.

One of the most common soft subgrade treatments is to cover the soft material with a geotextile wrapped granular fill. The granular fill typically comprises a well-graded coarse unbound granular material (for example, Type 2.5 material with B or C grading envelope in dry conditions, or Type 2.4 material with B or C grading envelope in wet conditions) or recycled material blend (for example, RM004 or RM005 material), or rock fill which has good inter-particle friction. The minimum thickness of granular fill material typically required is as shown in Table 3.14.1.

Rock fill is typically covered by a 150 mm heavily bound (cemented) material or lightly bound improved layer to provide a stable platform for construction of the pavement. Where rock fill is used to treat soft subgrades, the issues listed in Section 3.2.3 which may impact on future pavement performance should also be considered.

Table 3.14.1 – Typical minimum cover to provide a stable construction platform

Insitu Subgrade CBR at Time of Construction (%)

Typical Minimum Cover of Granular Fill to Provide a Stable Construction Platform (mm)

1.0 – 1.4 400

1.5 – 1.9 300

2.0 – 2.4 200

2.5 – 2.9 150

Note:

Cover thicknesses in this table assume a typical level of construction traffic required for the sole purpose of constructing the overlying pavement layers.

The characterisation of the coarse granular materials and rock fill used in soft subgrade treatments for pavement design purposes is typically consistent with the guidance provided in Section 5.9

3.14.2 Improved layers under bound layers

Addition

An improved layer is typically included under pavements with asphalt, heavily bound (cemented), and/or concrete layers. An improved layer is also typically included under foamed bitumen stabilised material where the subgrade design CBR is less than 7%. The improved layer is in addition to the soft subgrade treatments detailed in Sections 3.14.1 and 5.9.



The improved layer:

• provides access for construction traffic and minimises the potential for rainfall to cause subgrade instability and excessive construction delays

• provides a sound platform on which to construct the pavement layers (to achieve compaction), and

• protects the subgrade and supports the pavement for the life of the pavement structure.

Asphalt, heavily bound (cemented) and concrete pavements

For asphalt, heavily bound (cemented) and concrete pavements with design traffic of 1000 ESA/day or more at opening, the improved layer typically consists of a 150 mm (minimum) thick layer of lightly bound material with an unconfined compressive strength of 1.0 to 2.0 MPa at seven days (MRTS10 Plant-Mixed Lightly Bound Pavements).

For these pavements, a minimum support condition also applies, which is detailed in Section 8.2.8 for asphalt and heavily bound (cemented) pavements, and Section 9.3.1 for concrete pavements.

In lower-trafficked pavements, a Type 2.3 unbound granular material or RM003 recycled material blend improved layer is typically adopted.

A more substantial treatment may be needed where:

• the insitu strength of the underlying material is less than CBR 7% (at the time of construction)

• traffic using the improved layer prior to placement of the next structural layer exceeds 1 x 10³ ESA, and/or

• required by the contractor for the particular site and construction procedures used.

For unbound and lightly bound improved layers, it is typical practice to prime and seal (10 mm, C170) the improved layer in the following situations:

• where rainfall during construction of the improved layer and/or pavement is likely

• where part of the curing strategy for a lightly bound improved layer

• where the improved layer is exposed to the environment (that is, not covered within a few days of construction) and/or trafficked for an extended period of time, and/or

• the improved layer is permeable and/or the layer(s) below the improved layer are sensitive to the effects of moisture ingress.

For other situations the designer should consider the merits of priming and sealing the improved layer giving due consideration to the following:

• the cost of the treatment and impact of its inclusion in the design on the construction program

• the need for an alternative curing method for the improve layer prior to covering

• damage to the improved layer by construction traffic and the environment

• infiltration of moisture into the subgrade, and

• the program risk and costs associated with construction delays and rework.

Where sealing of the improved layer is omitted, a prime is typically still included except where the pavement is constructed in a single shift to meet traffic management constraints.



An initial seal (formerly known as a primerseal) may also suffice in some circumstances, where this has been determined to provide a suitable surface for trafficking, and waterproofing for construction operations. However, the effect of cutter in the initial seal on subsequent pavement layers needs to be considered.

Refer to Transport and Main Roads Technical Note TN175 Selection and Design of Sprayed Bituminous Treatments for further guidance.

The improved layer is included in the mechanistic-empirical pavement design. Further details on design inputs are included in Tables 6.2.3(b) and 6.8 for unbound and lightly bound improved layer materials.

Foamed bitumen stabilised pavements

For pavements comprising foamed bitumen stabilised granular material, an improved layer of unbound granular material (minimum 100 mm) or fill (minimum thickness as specified in MRTS04 General Earthworks) is typically provided where the design subgrade CBR is less than 7%.

For these pavements, a minimum support condition also applies, which is detailed in Section 8.2.8.

The improved layer in this case provides a platform on which to construct the foamed bitumen stabilised granular layers, and assists in protecting the subgrade. However, at the typical design configurations shown in Tables 2.2.9(a) to 2.2.9(c), this treatment may provide only limited access for construction traffic and limited protection from rainfall during construction. For plant-mixed foamed bitumen stabilised pavements, these functions are typically achieved with the first foamed bitumen stabilised granular layer (minimum 150 mm) placed above the improved layer (or above the subgrade where there is no improved layer).

It is typical practice to seal (with no prime) between foamed bitumen stabilised granular layers in the following situations:

• where rainfall during construction of the foamed bitumen stabilised granular layers is likely

• where the lower foamed bitumen stabilised granular layer is exposed to the environment (that is, not covered within a few days of construction) and/or trafficked for an extended period of time, and/or

• the lower foamed bitumen stabilised granular layer is permeable and/or the layer(s) below it are sensitive to the effects of moisture ingress.

Where foamed bitumen stabilised granular layers are exposed to an extended period of construction traffic and/or public traffic, fatigue damage due to the traffic must be taken into consideration in the pavement design, as detailed in Section 3.11.

The improved layer is included in the mechanistic-empirical pavement design. Refer to Section 6.7 for guidance on design inputs for the foamed bitumen stabilised granular layers.

3.15 Surfacing type

3.15.1 Sprayed seals

Addition

Wherever possible, a prime and seal is typically adopted, rather than an initial seal (formerly known as a primerseal), due to the likelihood of enhanced bonding with the underlying pavement. An exception to this is over foamed bitumen stabilised material where an initial seal should be used. An initial seal



may also be used in some other situations, such as where this risk is considered less important than the imperative that the pavement be opened to traffic soon after construction or that the pavement be constructed under traffic.

3.15.3 Open-graded asphalt

Addition

Initial construction

A 10 mm or 14 mm dense graded asphalt intermediate course is typically provided under open graded asphalt. Provision of this course enables the open graded asphalt to be fully removed without unduly disturbing the underlying pavement when resurfacing is required.

3.17 Settlement

New

Neither AGPT02 nor this supplement contain provisions for settlement of materials below the pavement layers. Where required, additional geotechnical investigations and assessments should be carried out to determine if and how much settlement may occur. The amount of settlement permissible typically varies for different pavement types and maintenance strategies. If unacceptable settlement is likely, pre-treatment (for example, drainage and/or surcharge of the formation) may be required to reduce the magnitude and extent of settlement after the pavement is constructed.

Settlement criteria for maximum total in-service settlement and maximum differential settlement are included in the Transport and Main Roads Geotechnical Design Standard – Minimum Requirements (2015).

3.18 Pavement jointing considerations

New

The structural competency of the pavement at longitudinal construction joints is often not as sound as in other areas. As a result, pavements tend to be weaker and more permeable at longitudinal construction joints. Load induced deformation and/or cracking can occur in these areas.

To reduce the risk of premature distress, construction joints are typically located away from wheel paths. Additionally, construction joints in flexible pavement layers are typically offset from the construction joints in underlying layers using a step-type arrangement.

3.19 Thickness of bituminous seals

New

For the purpose of determining design levels, the thickness of seals and initial seals (formerly known as primerseals) should be taken as the Average Least Dimension (ALD) of the cover aggregate. If the ALD is not known at the time of design, the ALD can be estimated as 6 mm for 10 mm nominal size cover aggregate and 9 mm for 14 mm nominal size cover aggregate.

3.20 Temporary pavements for high traffic

New

In order to facilitate traffic management, it may be necessary to utilise temporary pavements during construction.



Unbound granular pavements are considered to be very high risk for temporary pavements in high traffic situations (1000 ESA/day or more in the design lane), and are therefore not typically adopted in such situations. A number of projects have suffered failures of unbound granular pavements within the first day of trafficking, resulting in significant interruptions to road users and the project program. Therefore, temporary connections for pavements in high traffic situations typically comprise, as a minimum, a heavily bound (cemented) base with asphalt surfacing. An improved layer is typically provided below the heavily bound (cemented) base where the subgrade design CBR is less than 5%, and/or where required to facilitate construction of overlying pavement layers.

Other temporary pavement alternatives that have been successfully used in high traffic situations include asphalt over granular (AG(A)), asphalt over heavily bound (cemented) pavement (ASt(A)) and full depth asphalt.

4 Environment

4.1 General

Addition

Historical climate data is used to assist with site classification, including the likely moisture and temperature conditions the pavement will experience in service. Further information on climate zones and average conditions is available from the Commonwealth Bureau of Meteorology at www.bom.gov.au.

Figure 4.1 illustrates Australian climatic zones on the basis of temperature and humidity. Most of coastal Queensland is classified as having hot humid summers. Western areas have hot summers with either mild or cold winters.

Figure 4.1 – Australian climatic zones (www.bom.gov.au)

http://www.bom.gov.au/




4.2 Moisture environment

Addition

The moisture environment will have an impact on subgrade moisture conditions, drainage requirements and the selection of pavement materials. Volume changes and material strength variations caused by moisture content changes can lead to cracking and, when loaded, shear failures in subgrades and paving materials.

Figure 4.2(a) illustrates Australian seasonal rainfall zones, based on median annual rainfall and seasonal incidence. Figure 4.2(b) provides more detail for Queensland, illustrating median annual isohyets. Rainfall intensity may also impact on moisture conditions within the pavement and subgrade.

Figure 4.2(a) – Australian seasonal rainfall zones (www.bom.gov.au)




Figure 4.2(b) – Median annual isohyets for Queensland

4.3 Temperature environment

Addition

WMAPTs for additional sites in Queensland are listed in Appendix B of this supplement.

Transport and Main Roads technical specifications place limits on temperatures and weather conditions for placing pavement layers. These requirements limit the detrimental effects that adverse weather conditions can have on the quality and/or performance of the constructed pavement.



5 Subgrade evaluation

5.1 General

Addition

MRTS04 General Earthworks includes requirements for assessment of subgrade materials.

In addition to assessing subgrade strength, evaluation of the expansive nature of subgrade materials is also important.

5.3 Factors to be considered in estimating subgrade support

Addition

Subgrade materials are typically assessed using the following measures:

• soil description and classification

• plasticity (plastic limit, liquid limit, and plasticity index)

• moisture content insitu

• particle size distribution

• Weighted Plasticity Index (WPI), which is the plasticity index multiplied by the percent passing the AS 0.425 mm sieve

• laboratory CBR and swell determined at the design density and moisture conditions, and

• field CBR tested with a Dynamic Cone Penetrometer (DCP).

When stabilisation of the subgrade material is being considered, additional testing may also be required such as lime demand, sulphate content and UCS. Further guidance on the evaluation of materials for stabilisation is provided in the Transport and Main Roads Pavement Rehabilitation Manual, Transport and Main Roads Technical Note TN149 Testing of Materials for Insitu Cement or Cementitious Blend Stabilisation and Transport and Main Roads Technical Note TN151 Testing of Materials for Lime Stabilisation.

5.3.5 Moisture changes during service life

Addition

Expansive soils

As a consequence of changes in water content, subgrades with expansive soils (including embankments where expansive soils have not been excluded), can experience considerable volume change that can disrupt the pavement in a number of ways, including:

• surface deformation, causing roughness and potential ponding of water

• pavement deformation, that can cause loss of density and loss of strength, and

• cracking that can allow the infiltration of contaminants (such as water and incompressible material) and also loss of strength.

The magnitude of volume change depends on factors such as:

• expansive nature of the subgrade and/or embankment material

• extent (width and depth) of expansive material



• changes in moisture content related to climatic conditions, which are often expressed in terms of the depth of design soil suction change

• effectiveness of adopted treatments

• material density and permeability, and

• changes in moisture content related to local site conditions (such as drainage provisions).

For the classification of expansive soils, Table 5.2 in AGPT02 is replaced by Table 5.3.5. Where CBR swell and Weighted Plasticity Index (WPI) on the same material indicate different classifications, the CBR swell should take precedence.

Table 5.3.5 – Guide to classification of expansive soils

Expansive Nature Weighted Plasticity Index (WPI) (PI x % < 0.425 mm) CBR Swell (%)1

Extreme > 4200 > 10.0

Very high 3200 – 4200 5.0 –10.0

High 2200 – 3200 2.5 – 5.0

Moderate 1200 – 2200 0.5 – 2.5

Low < 1200 < 0.5

Notes:

1. Swell at OMC, 95% to 98% MDD (standard compactive effort), four-day soaked, and using 4.5 kg surcharge. The degree to which volume change is addressed in the design solution depends on a number of project-specific factors such as:

• cost of initial treatment alternatives

• impact of initial treatment alternatives on function and serviceability

• availability of materials

• tolerance for future maintenance interventions to correct loss of shape and/or cracking in the pavement, and

• project constraints such as time and traffic management.

Where expansive subgrades are present, a geotechnical assessment is typically required to determine the appropriate mitigation strategy, particularly where the depth of design soil suction change is very high and/or the expansive nature of the soil is extreme (as defined in Table 5.3.5).

Providing a minimum cover of material over expansive soil is one of the most common techniques used to minimise volume change impacts on the pavement. The required thickness of cover is an output of the geotechnical assessment.

Fox (2000 and 2002) defines the relationship between the depth of design soil suction change and six climatic zones in Queensland: wet coastal, wet temperate, temperate, dry temperate, semi-arid and arid. The depth of design soil suction change is considered to be very high in dry temperate, semi-arid and arid areas. In these areas, providing a minimum cover of material over expansive soil is not typically economic as substantial thicknesses of cover are required. In these areas, other treatments



are typically adopted and these are selected and designed in accordance with local practice (for example, lime stabilisation).

For pavements over embankment fill materials that are expansive in nature, cover and zoning requirements should meet the requirements of MRTS04 General Earthworks.

For pavements over existing insitu subgrade material (such as in cuttings, at grade, or under low / near grade embankments) with an expansive nature which is high or very high (as defined in Table 5.3.5), and where a geotechnical assessment is not undertaken, the following guidance should be used to determine the cover thickness:

• for flexible pavements, the thickness as determined from Figure 5.3.5 (which includes the thickness of the pavement and other courses such as select fill, rock fill, treated material and improved layers). Figure 5.3.5 assumes that a minimum 150 mm layer of low-permeability subbase, improved layer or select fill is included in the overall structure

• for rigid pavements, a minimum cover of 600 mm over highly expansive subgrades and 800 mm over very highly expansive subgrades (to the underside of the subbase), including a minimum 150 mm of low permeability material.

These thicknesses only apply in wet coastal, wet temperate and temperate locations where the depth of design soil suction change is 2.3 metres or less (corresponding to locations with Thornthwaite Moisture Index of -15 or greater). In dry temperate, semi-arid and arid locations, where the depth of design soil suction change is greater than 2.3 metres (corresponding to Thornthwaite Moisture Index less than -15), a project-specific geotechnical assessment is recommended. Refer to AS 2870 and Fox (2000 and 2002) for further guidance.

Additionally, these thicknesses are intended to mitigate the risk based on the importance of the road (for example, low risk for heavily trafficked pavements, and higher risk for lower trafficked pavements). However, it may not always be economic to provide these cover thicknesses, particularly for pavements with low traffic and where suitable fill materials are not readily available. In such circumstances, a design solution that accepts the potential impacts and addresses these through appropriate maintenance may be necessary.

For pavements over existing insitu subgrade material with a low or moderate expansive nature (as defined in Table 5.3.5), additional cover beyond that provided by the pavement and support layers is not typically required.



Figure 5.3.5 – Typical cover thickness over highly and very highly expansive material for flexible pavements (thickness includes the pavement)

The following additional strategies may also be adopted, as appropriate, to aid in minimising volume change in expansive soils:

• in embankments, limit the use of highly expansive materials to the core zone (that is, use zoned embankments as detailed in MRTS04 General Earthworks)

• control the moisture content of the top 300 mm of the untreated subgrade prior to and during the placement of overlying layers, so that the moisture content after placement of the pavement is as near as possible to the equilibrium moisture content

• direct water away from the formation by adopting appropriate geometric design (for example, maximising gradient and crossfall), and/or by adopting drainage provisions that avoid pondage of water within 5 m of the formation

• make provision for drying back and re-compacting water-affected subgrades

• in arid and semi-arid environments:

o provide flat embankment batters using low permeability materials (1 on 4 or flatter) and low formation height, wherever possible, as it has been found that shoulder and pavement edge cracking and deformation are more prone to occur as fill height increases and where batters are steeper

o maintain positive formation height above the surrounding terrain (say 300 – 500 mm at the top of pavement at formation edge with subgrade level being at least 100 mm above the surrounding terrain), and

o provide table drains where positive drainage is possible.



Geotechnical assessment

A geotechnical assessment typically involves consideration of the following information:

1. Test results for the following material properties:

• liquid limit, plasticity index, grading (including determining the percentage of material passing the 2 µm sieve) and weighted plasticity index

• shrink-swell index

• moisture content (including variations in moisture content with depth)

• suction, and

• clay type (typically determined using x-ray diffraction).

Samples are typically obtained using shallow boreholes with continuous undisturbed sampling.

2. Maintenance history and condition of existing pavements and structures located where similar soils and moisture conditions are present.

3. Moisture conditions expected at the site, including potential for the material to wet up and dry out during construction and throughout the life of the pavement.

4. Transport and Main Roads performance expectations for the pavement.

Based on the above information, a geotechnical engineer can provide guidance on an appropriate thickness of cover noting:

• unbound granular, full depth asphalt and CRCP are better able to withstand subgrade movements than other pavement types

• asphalt shape correction treatments typically are not suitable for jointed pavements (PCP and JRCP)

• recompacted clays may have a higher potential for movement (in the first few years of wetting and drying cycles) than undisturbed clay subgrades, and

• procedures for estimating surface movement such as those outlined in AS 2870 and Van der Merwe (1964).

5.3.8 Lime-stabilised subgrades

Difference

The mix design procedure for lime-stabilised subgrades is detailed in Transport and Main Roads Technical Note TN151 Testing of Materials for Lime Stabilisation.

Guidance on the design of pavements with lime-stabilised subgrades is provided in Transport and Main Roads Technical Note TN74 Structural Design Procedure of Pavements on Lime Stabilised Subgrades.

5.6 Laboratory determination of subgrade CBR and elastic parameters

Addition

The typical pretreatment for materials that breakdown under environmental and service conditions due to weathering (such as shales, claystones, siltstones and other soft laminated or jointed rocks), is to



precondition the materials by artificial weathering (10 cycles of soaking for at least 16 hours followed by drying on a hot plate without baking).

For material susceptible to breakdown due to construction procedures and weathering, typical pretreatment involves artificial weathering followed by repeated cycles of compaction.

5.6.1 Determination of density for laboratory testing

Addition

The compaction standard for CBR testing is typically aligned with the compaction requirements in MRTS04 General Earthworks. For existing subgrade (as defined in MRTS04 General Earthworks) and fill material, a compaction standard of 95% (standard compaction) is typically adopted for CBR testing.

5.6.2 Determination of moisture conditions for laboratory testing

Addition

Site specific information and/or local knowledge is preferred for determining the moisture content to be used. A guide to typical moisture conditions for laboratory CBR testing of subgrade materials is provided in Table 5.6.2.

Table 5.6.2 – Guide to moisture conditions for laboratory CBR testing

Location / Circumstances Testing Condition

Locations where all the following are true: • median annual rainfall ≤ 800 mm • excellent surface drainage and waterproofing • excellent subsurface drainage • subgrade not significantly affected by the water table,

standing water, or ponded water • subgrade not affected by inundation regularly and/or for

extended periods • experience indicates that unsoaked conditions should

apply

Unsoaked

Locations where any of the following are true: • floodways, causeways and other pavements likely to be

inundated regularly and/or for extended periods • cuttings at or below the water table level that existed prior

to the cutting and/or where seepage is likely • situations where experience indicates that 10 day soaked

conditions should apply

10 day soaked

Locations with circumstances not described above, and where experience indicates that 4 day soaked conditions should apply 4 day soaked

Where unsoaked CBR testing is adopted, an investigation into the sensitivity of the material strength to moisture content variations is typically undertaken. For moisture sensitive materials, this typically includes CBR testing at a range of moisture contents and densities. The results of such testing may indicate the need to adopt a CBR that differs from the reported test results (multi-point CBR test results are typically reported at OMC and MDD).



The following points are provided as a guide to the moisture sensitivity of various materials:

• Sandy (SW, SP) soils – small fluctuations in water content produce little change in volume or strength / stiffness.

• Silty (SM, SC, ML) soils – small fluctuations in water content produce little change in volume, but may produce large changes in strength / stiffness. Typically these soils attract and retain water through capillary action, and do not drain well.

• CL or CH clay – small fluctuations in water content may produce large variations in volume, and there may be large changes in strength / stiffness, particularly if the moisture content is near or above optimum. Typically these soils attract and retain water through matrix suction.

5.7 Adoption of presumptive CBR values

Addition

Use of presumptive values typically involves the assessment of subgrades on the basis of geological, topographic and drainage information, routine soil classification tests and performance for similar soils in similar conditions. Once these factors are assessed, it may be possible to assign a presumptive design CBR. Use of presumptive values is typically limited to lightly-trafficked pavements.

5.9 Subgrades with design CBR less than 3%

New

This section applies when the design subgrade CBR is less than 3% (at the design moisture and density conditions). This is distinguished from when the insitu CBR of the subgrade at the time of construction is less than 3%, which is addressed in Section 3.14.1.

For unbound granular pavements, a design subgrade CBR less than 3% may be used as an input into Figures 8.4 and 12.2 of AGPT02.

For flexible pavements with one or more bound layers, and for rigid pavements, a soft subgrade treatment that results in a presumptive subgrade design CBR of at least 3% is typically provided where the subgrade design CBR would otherwise be less than 3%. A presumptive subgrade design CBR is then adopted in the pavement design calculations which accounts for the combined strength of the soft subgrade and the soft subgrade treatment.

The presumptive design CBR should be determined by considering the treatment and the likely long-term condition of the materials and subgrade. For example, a presumptive subgrade design CBR of 3% for the assumed semi-infinite layer (that is, from the top of the treatment and extending infinitely below) is typically adopted for the following treatments:

• geotextile wrapped granular material, comprising either coarse unbound granular material (for example, Type 2.5 material with B or C grading envelope in dry conditions, or Type 2.4 material with B or C grading envelope in wet conditions), recycled material blend (for example, RM004 or RM005 material) or rock fill (MRTS04), with thickness determined using Table 5.9.

• a minimum 200 mm of Category 1 or 2 heavily bound (cemented) material over subgrade material with a design CBR of 2 to 3%

• a minimum 150 mm of mass concrete (either lean-mix concrete or no fines concrete with geotextile) or sand / cement (12:1) mix over subgrade material with a design CBR of 2 to 3%.



Use of heavily bound (cemented) material or mass concrete may be difficult if the insitu CBR of the subgrade at the time of construction is also less than 3%.

Table 5.9 - Minimum thickness of coarse granular or rock fill required for the adoption of a presumptive design CBR of 3%

Subgrade CBR (%) (At Design Density and Moisture Conditions)

Minimum Thickness (mm) of Coarse Granular or Rock Fill Required for the

Adoption of a Presumptive Design CBR of 3%

1.0 400

1.5 300

2.0 200

2.5 150

3.0 0 In assigning design parameters (for both flexible and rigid pavement design) to the materials used in soft subgrade treatments, consideration should be given to the impacts of construction traffic and long-term service, recognising that the long-term condition of such materials is likely to be significantly degraded from their initial condition. Typically the materials (including granular, rock fill, and heavily bound (cemented) materials) are modelled as selected subgrade materials with design parameters not exceeding those of a CBR 15% selected fill material.

Rock fill is typically covered by a 150 mm heavily bound (cemented) material or lightly bound improved layer to provide a stable platform for construction of the pavement. Where rock fill is used to treat soft subgrades, the issues listed in Section 3.2.3 which may impact on future pavement performance should also be considered.

6 Pavement materials

6.1 General

Addition

Recycled materials may be used as a substitute for new materials in unbound, lightly bound, heavily bound (cemented) and foamed bitumen stabilised pavement layers, as detailed in the relevant technical specifications.

6.2 Unbound granular materials

6.2.1 Introduction

Addition

Material characteristics and requirements

The quality and strength requirements for unbound granular paving materials depend upon a combination of factors including:

• traffic loading

• climate, and

• pavement configuration and drainage.



The performance of unbound pavements is heavily influenced by the moisture content, or more specifically, the degree of saturation of the material. Where the degree of saturation limit of the material is exceeded, the permanent deformation resistance of the material reduces significantly, often resulting in rapid failure under traffic. For this reason it is essential that unbound granular materials be dried back to a moisture content less than the material’s degree of saturation limit prior to sealing, and maintained such that the degree of saturation limit is not exceeded during service.

Table 6.2.1 provides a guide to the selection of standard materials for use in unbound granular pavements with thin bituminous surfacings, based on traffic loading and median annual rainfall. Selection and specification of unbound granular materials also requires consideration of project-specific factors such as:

• site conditions such as perched water tables, flat terrain, restricted surface drainage, weather conditions, inundation etc. may cause a greater exposure to water than represented by the median annual rainfall category

• availability of materials

• drainage provisions, recognising it is essential for all unbound granular materials to be adequately drained, including surface, side and subsurface drainage

• quality control provisions, in particular source rock selection and other quarry management practices, and aggregate production testing regimes and associated use of control measures such as statistical control charts

• contract administration arrangements, in particular auditing and surveillance in relation to source material and product quality

• the need to protect moisture sensitive or expansive subgrades by specifying materials with low permeability

• coarse graded materials, particularly those with low clay contents, are permeable and prone to segregation

• gap graded materials are more permeable and prone to segregation than coarse graded materials but can be used with additional care

• well graded material with appropriate fine material properties may provide the best overall service but may be more expensive

• fine graded materials and/or materials with excess fines have less permeability and are less prone to segregation but may require additional attention to achieve their specified CBR requirement, and

• pavement performance and maintenance expectations.



Table 6.2.1 – Typical application of standard materials in unbound granular pavements with thin bituminous surfacings

Average Daily Traffic in Design Lane in Year of Opening

(ESA)

Typical Material Type (MRTS05)1,2,3

Median Annual Rainfall (mm)

≥ 800 mm / Year ≥ 500 mm / Year to < 800 mm / Year < 500 mm / Year

Base

≥ 1000 to < 3000 1 (HSG)4 1 (HSG) 4 1 (HSG) 4

≥ 100 to < 1000 2.1 2.1 or 3.1 3.1

10 to < 100 2.1 2.1 or 3.1 3.1

< 10 2.2 2.2 or 3.2 3.2

Upper Subbase

≥ 1000 to < 3000 2.3 2.3 or 2.4 2.3, 2.4, 3.3 or 3.4

≥ 100 to < 1000 2.3 2.3, 2.4, 3.3 or 3.4 3.3 or 3.4

< 100 2.4 2.4 or 3.4 3.4

Lower Subbase

All 2.5 2.5 or 3.5 3.5

Notes:

1. Recycled material blends may also be used, as detailed in MRTS35 Recycled Materials for Pavements.

2. Where material type alternatives are given, the first is the preferred and typically adopted option, with other materials listed in order of preference.

3. The requirements for Type 3 materials in MRTS05 Unbound Pavements do not include any minimum durability requirements, and therefore site specific moisture conditions should be carefully considered in addition to median rainfall.

4. The decision to use Type 1 (HSG) material is typically based on a project-specific assessment. Refer to Transport and Main Roads Technical Note TN171 Use of High Standard Granular (HSG) Bases in Heavy Duty Unbound Granular Pavements for further guidance.

6.2.3 Determination of modulus of unbound granular materials

Addition

Presumptive values

The following may be used as a guide when assigning maximum design modulus values to typical granular materials:

a) under thin bituminous surfacings – Table 6.2.3(a)

b) in subbase / improved layers under bound pavements – Table 6.2.3(b)

c) when lightly bound in base and improved layers – Table 6.8.



Table 6.2.3(a) – Presumptive values for elastic characterisation of unbound granular base materials under thin bituminous surfacings

MRTS05 or MRTS35 Material Type Presumptive Vertical Modulus of Top Sublayer (MPa)

1 (HSG) 500

2.1, 3.1, RM001 350

2.2, 3.2, RM002 300

Table 6.2.3(b) – Presumptive values for elastic characterisation of unbound granular materials used as subbase / improved layer under bound pavement layers

MRTS05 or MRTS35 Material Type1 Presumptive Vertical Modulus of Top Sublayer (MPa)

2.3, 2.4, 3.3, 3.4, RM003, RM004 150

Notes:

1. Where Type 2.1 or RM001 material is used, the presumptive modulus is determined using Table 6.4 of AGPT02. Where Type 1 (HSG) material is used, the presumptive modulus is determined using Table 6.5 of AGPT02.

6.3 Modified granular materials

Addition

Modified granular materials as defined in AGPT02 (with a maximum 28 day UCS of 1.0 MPa) are not commonly used on Transport and Main Roads projects. Where small amounts of stabilising agents are used, typically these are specified with a UCS between 1.0 and 2.0 MPa, and are referred to as lightly bound materials. Further detail on lightly bound granular materials is provided in Section 6.8.

6.4 Cemented materials

6.4.1 Introduction

Addition

Main characteristics

Guidance on lightly bound materials (with UCS of 1.0 to 2.0 MPa) is included in Section 6.8.

The typical characteristics of heavily bound (cemented) materials supplied to Transport and Main Roads technical specifications are as follows:

• Category 1 materials typically produce wider shrinkage cracks, which will be more prone to reflection into overlying layers, than cracks in Category 2 materials.

• Higher standard unbound granular materials in the heavily bound (cemented) layer should produce narrower and more closely spaced shrinkage cracks, which will be less prone to reflection through overlying layers, and

• Category 1 materials may be less prone to erosion and crushing than Category 2 materials. Erosion resistance becomes increasingly important for pavements which are subjected to higher traffic volumes and/or higher rainfall.



The presence of high traffic volumes and/or high moisture ingress can cause rapid erosion of material around cracks in the heavily bound (cemented) material.

Cracking of heavily bound (cemented) materials, and reflection of cracks into overlying layers, should always be anticipated when heavily bound (cemented) materials are adopted.

6.4.3 Determination of design modulus

Addition

Presumptive values

Presumptive values for the design modulus of heavily bound (cemented) materials typically adopted for standard Transport and Main Roads materials are provided in Table 6.4.3.

Table 6.4.3 – Presumptive values for elastic characterisation of standard heavily bound (cemented) materials

Material Category

Material to be Bound (MRTS05 or MRTS35 Type)

UCS (28 Day) (MPa)

Presumptive Design Modulus (MPa)1

Category 1 2.1 or RM0012 3.0 to 6.0 4,000

Category 2 2.1, 2.2, 3.13, 3.23 or RM0012 2.0 to 4.0 3,000

Notes:

1. These design modulus values assume seven days initial curing with negligible trafficking.

2. Refer to the relevant technical specifications for further guidance on the use of recycled materials.

3. Type 3 materials are only suitable for use in relatively dry environments (refer to Table 6.2.1).

6.4.8 Determining the in-service fatigue characteristics from presumptive flexural strength and modulus

Addition

Presumptive fatigue constants for heavily bound (cemented) materials typically adopted for standard Transport and Main Roads materials are provided in Table 6.4.8. These presumptive fatigue constants are for use with Equation 10 in AGPT02 (instead of Equation 15 in AGPT02) and the reliability factors in Table 6.8 of AGPT02.

Table 6.4.8 – Presumptive fatigue constants for standard heavily bound (cemented) materials

Property Category 1 Material Category 2 Material

Presumptive design modulus (MPa) 4,000 3,000

Presumptive flexural strength (MPa) 1.2 1.0

Presumptive in-service fatigue constant K 233 261 6.5 Asphalt

6.5.4 Determination of design modulus from direct measurement of flexural modulus

Addition

Transport and Main Roads Technical Note TN167 A New Approach to Asphalt Pavement Design provides further detail on the methodology for determining design modulus from direct measurement of flexural modulus for a specific asphalt mix.



Where the design modulus for a specific mix has been determined, it is used in conjunction with the fatigue model for the same mix, determined as detailed in Section 6.5.11.

6.5.5 Determination of design modulus from measurement of ITT modulus

Addition

A design modulus for a specific asphalt mix that has been determined from indirect tensile testing is not typically used on Transport and Main Roads projects. Determination of design modulus for a specific asphalt mix is typically undertaken using flexural modulus testing, as detailed in Section 6.5.4.

6.5.6 Design modulus from bitumen properties and mix volumetric properties

Addition

A design modulus for a specific asphalt mix that has been determined from bitumen properties and mix volumetric properties is not typically used on Transport and Main Roads projects. Determination of design modulus for a specific asphalt mix is typically undertaken using flexural modulus testing, as detailed in Section 6.5.4.

6.5.7 Design modulus from published data

Addition

Presumptive values of design modulus that are typically adopted for standard asphalt mixes are provided in Table 6.5.7(a) for a WMAPT of 32ºC. These values were generally derived from Indirect Tensile Test (ITT) results of Transport and Main Roads registered mix designs. For mix types where limited or no data was available, the presumptive design values were determined based on relationships with other mixes.

Except for open graded asphalt, design moduli for locations with a WMAPT other than 32ºC are calculated using Equation 6.5.7, rounded to the nearest multiple of 100 MPa.

[ ]( )( )3208.0

32,1000max −×−×= WMAPTCWMAPT eEE o (6.5.7)

where:

EWMAPT = asphalt modulus at the desired WMAPT (MPa)

E32ºC = asphalt modulus at WMAPT 32ºC (MPa)

WMAPT= desired WMAPT (ºC), as detailed in Appendix B of AGPT02

A modulus of 800 MPa is typically used for open graded asphalt for all WMAPTs and design speeds.



Table 6.5.7(a) – Presumptive values for elastic characterisation of asphalt mixes at a WMAPT of 32ºC

Asphalt Mix Type

Binder Type

Volume of Binder (%)

Asphalt Modulus at Heavy Vehicle Operating Speed (MPa)

10 km/h 30 km/h 50 km/h 80 km/h

OG10 A15E 9.5 800 800 800 800

OG14 A15E 8.5 800 800 800 800

SMA10 A15E 14.0 1000* (600)

1000* (900)

1100 1300

SMA14 A15E 13.0 1000* (600)

1000* (900)

1100 1300

AC10M C320 11.5 1000* (900)

1300 1600 1900

AC10M AC10H

A15E 11.5 1000* (600)

1000* (800)

1000 1200

AC14M C320 11.0 1100 1700 2000 2400

AC14M AC14H

C600 11.0 1400 2000 2400 2900

AC14M AC14H

A15E 11.0 1000* (700)

1000 1300 1500

AC20M C320 10.5 1200 1800 2200 2600

AC20M AC20H

C600 10.5 1500 2200 2600 3100

EME2 EME2 binder

13.5 2000 3000 3600 4200

Notes:

1. Indicated values (*) have been limited to a value of 1000 MPa. When adjusting these moduli to another WMAPT using Equation 6.5.7, E32ºC should be taken as the value in brackets.

In the absence of more reliable information about the heavy vehicle operating speed, presumptive operating speeds that are typically adopted for various designated speed limits are given in Table 6.5.7(b).

Table 6.5.7(b) – Presumptive heavy vehicle operating speeds

Project Location Presumptive Heavy Vehicle Operating Speed (km/h)

Flat to 5% Grade > 5% Grade

Speed limit > 80 km/h 80 50

Speed limit 50 – 80 km/h 50 30

Roundabouts, signalised intersections and approaches 30 10



6.5.9 Factors affecting asphalt fatigue life

Addition

Effect of binder type

Asphalt containing plastomeric polymer modified binder (for example, A35P) could be considered where improved deformation resistance is required, based on a project-specific engineering assessment. A35P provides improved deformation resistance when compared to A15E but is more prone to cracking. Therefore, A35P should only be used where the increased risk of cracking is accepted.

Where A35P is used, it is important to ensure sufficient support is provided to inhibit premature fatigue of the layer. Such support can be provided by including a heavily bound (cemented) subbase and/or using stiff underlying asphalt layers.

6.5.10 Fatigue criteria

Addition

Transport and Main Roads Technical Note TN167 A New Approach to Asphalt Pavement Design provides a methodology for determining a mix-specific fatigue relationship for use in pavement design. The mix-specific fatigue relationship can be used in place of the Shell laboratory model (equation 25 in AGPT02).

6.5.11 Means of determining asphalt fatigue characteristics

Addition

Transport and Main Roads Technical Note TN167 A New Approach to Asphalt Pavement Design provides a methodology for determining fatigue characteristics for a specific asphalt mix over a range of temperatures.

6.5.12 Permanent deformation of asphalt

Addition

Guidance on the selection of dense graded asphalt mix types and binders is included in Table 6.5.12.

As noted in Table 6.5.12, EME2 may be considered in base layers instead of dense graded asphalt, at all traffic levels as detailed in Tables 2.2.1, 2.2.5, 2.2.6(c) and 2.2.9(a).



Table 6.5.12 – Guide to the selection of dense graded asphalt (AC) mix type and binder class

Application

Traffic Volume (Average Daily ESAs in the Design

Lane in the Year of Opening) Dense Graded

Asphalt (AC) Mix Type1

Typical Binders

Free Flowing High Shear²

Top two asphalt layers in the pavement structure

< 1000 < 300 Medium duty C320

< 3000 < 1000 Medium duty C600³, M10004

All < 3000 Medium duty A15E5

≥ 1000 300 to < 3000 Heavy duty C600³, M10004

≥ 3000 ≥ 1000 Heavy duty A15E

Layers covered by at least two layers of asphalt

< 3000 < 1000 Medium duty C320

All < 3000 Medium duty C600, M1000

All All Medium duty A15E

≥ 3000 ≥ 1000 Heavy duty C600

Notes:

1. EME2 may be considered in base layers instead of dense graded asphalt, at all traffic levels as detailed in Tables 2.2.1, 2.2.5, 2.2.6(c) and 2.2.9(a).

2. High shear areas include signalised intersections and approaches, roundabouts and approaches, and other areas with very slow moving and/or stationary heavy vehicles.

3. C600 is generally not used in the surfacing course.

4. M1000 typically has a shorter oxidation life than C320 and A15E binders. More frequent resurfacing should be anticipated where M1000 binder is used in surfacing layers. Presumptive design parameters for Transport and Main Roads registered mixes with M1000 binder have not been established. For these reasons, M1000 is not typically used unless approved by the Transport and Main Roads project representative.

5. A15E binder is typically used in situations where enhanced deformation and/or fatigue resistance is desired. 6.6 Concrete

6.6.4 Base concrete

Addition

A design flexural strength of 4.5 MPa (at 28 days) is typically adopted for pavement quality base concrete. For steel-fibre reinforced concrete, a design flexural strength of 5.5 MPa (at 28 days) is typically adopted.

6.7 Foamed bitumen stabilised materials

New

Guidance on material requirements, material characterisation (for pavement design) and mix design of foamed bitumen stabilised materials is provided in the Transport and Main Roads Pavement Rehabilitation Manual, Transport and Main Roads Technical Notes TN150 Testing of Materials for Insitu Foamed Bitumen Stabilisation and TN179 Testing of Materials for Plant-mixed Foamed Bitumen Stabilisation, Part 5: Pavement Evaluation and Treatment Design of the Austroads Guide to Pavement Technology (Austroads, 2011) and relevant technical specifications.



The following points also apply in relation to determination of the design modulus of the foamed bitumen stabilised material:

a) The full thickness of the foamed bitumen stabilised material is assigned the same design modulus according to the aforementioned documents (the design modulus is mix-dependent, and is between 1800 MPa and 2500 MPa at 25ºC prior to temperature correction).

b) Where the overlying asphalt thickness is greater than or equal to 100 mm, temperature correction does not apply.

c) Where the overlying asphalt thickness is less than 100 mm, temperature correction applies using the factors in Table 6.7.

Table 6.7 – Temperature correction factors for determination of foamed bitumen stabilised material design modulus

WMAPT (ºC)1 Temperature Correction Factor (Ft)

< 50 mm Overlying Asphalt 50 to < 100 mm Overlying Asphalt

≤ 25 1.00 1.00

30 0.90 0.95

35 0.80 0.90

40 0.70 0.85

Notes:

1. For intermediate temperatures, linear interpolation is used to determine the temperature correction factor. 6.8 Lightly bound granular materials

New

Lightly bound granular materials are typically specified to have a UCS between 1.0 and 2.0 MPa at 28 days when used in lightly bound base layers, and 1.0 to 2.0 MPa at seven days when used in lightly bound improved layers.

While this approach may result in a material that is more prone to fatigue and/or shrinkage cracking than cement modified materials (with maximum 28 day UCS of 1.0 MPa, as defined in AGPT02), it has a number of benefits which include:

• reduced moisture sensitivity

• higher strength and stiffness

• reduced permeability

• reduced erodability

• reduced sensitivity to variations in grading and plasticity, and

• higher binder content is more readily and consistently achieved.

To alleviate some of the concerns relating to cracking when used in base courses, Transport and Main Roads typically adopts additional controls such as:

• SAM / SAMI seals over the lightly bound base

• minimum 200 mm total thickness of lightly bound base



• minimum support conditions, as detailed in Section 8.2.8.

Lightly bound granular materials are typically modelled in the same way as unbound granular materials (sub-layered and cross-anisotropic with a degree of anisotropy of 2), with a Poisson’s Ratio of 0.35 and presumptive vertical modulus of the top sublayer as listed in Table 6.8.

Table 6.8 – Presumptive values for elastic characterisation of lightly bound granular materials

MRTS10 Material Type Presumptive Vertical Modulus of Top Sublayer (MPa)

Lightly bound base Refer to Table 6.5 of AGPT02

Lightly bound improved layer / subbase 210 When using lightly bound granular materials, the risks of both shrinkage and fatigue cracking should be recognised and accepted, and associated maintenance interventions over the life of the pavement should be anticipated.

7 Design traffic

7.4 Procedure for determining total heavy vehicle axle groups

7.4.2 Selection of design period

Addition

The design periods typically adopted by Transport and Main Roads are as detailed in Table 7.4.2.

Table 7.4.2 – Typical design periods

Annual Average Daily Traffic (AADT) (Total in Two Directions) Typical Design Period (Years)

≥ 30,000 30

< 30,000 20 The design period may be optimised for project-specific requirements, which would typically involve consideration of whole-of-life costs and the infrastructure investment strategy current at the time of the design.

7.4.4 Initial daily heavy vehicles in the design lane

Addition

Designers are referred to the Traffic Surveys and Data Management (TSDM) web reporting tool as a source of traffic data such as Traffic Analysis and Reporting System (TARS) and Weigh-In-Motion (WIM) reports. Transport and Main Roads officers can access TSDM at https://www.tap.qdot.qld.gov.au/tsdm/html/tsdm-index.html.

The traffic volume in the year of opening may be determined by multiplying traffic volumes from a previous year (for example, the year the traffic survey was undertaken) by a growth factor (GF) as shown in Equation 7.4.4(a).

https://www.tap.qdot.qld.gov.au/tsdm/html/tsdm-index.html



( )xRGF ×+= 01.01 (7.4.4(a))

where:

R = heavy vehicle growth rate per annum (%)

X = time period (years) between the year of the traffic survey and year of opening.

The average daily ESA in the design lane in the year of opening (ESA/day) can be calculated using Equation 7.4.4(b).

𝐸𝐸𝐸𝐸𝐸𝐸 𝑑𝑑𝑑𝑑𝑑𝑑⁄ = 𝑁𝑁𝑖𝑖 × 𝑁𝑁𝐻𝐻𝐻𝐻𝐻𝐻𝐻𝐻 × 𝐸𝐸𝐸𝐸𝐸𝐸𝐻𝐻𝐻𝐻𝐸𝐸𝐻𝐻� (7.4.4(b))

Where Ni, and NHVAG are as detailed in Sections 7.4.4, 7.4.7 and 7.6.2 of AGPT02.

7.4.5 Cumulative number of heavy vehicles when below capacity

Addition

The heavy vehicle growth rate is typically estimated based on project-specific traffic counts, historic trends and, in some cases, traffic modelling.

An additional source of information is Report 121 of the Department of Infrastructure and Transport, Road Freight Estimates and Forecasts in Australia: interstate, capital cities and rest of state (BITRE, 2010). This report includes estimates of growth based on a comprehensive study of historic growth, and expected economic and population growth. The growth rates in Table 7.4.5 were calculated using the information published in Report 121 and provide an indication of the likely growth, based on freight forecasts, for various general types of freight routes. These values are presumptive only and are not intended to replace sound project-specific information.

Table 7.4.5 – Presumptive growth rates for below capacity traffic flow based on freight forecasts

Road Presumptive Annual Growth (2013 to 2020) (%)

Presumptive Annual Growth (2021 onwards) (%)

Highways, motorways and other interstate routes

5 3

Urban roads in and around Brisbane, other than interstate routes

4 2

Other state controlled roads 3 2

Where guidance in this supplement is based on the average daily ESA in the design lane in the year of opening, it is assumed that heavy vehicle growth rates are not excessive when compared to typical historic rates. In this regard, heavy vehicle growth rates exceeding about 10% per annum may be considered excessive.

7.4.6 Cumulative number of heavy vehicles considering capacity

Addition

Consideration should be given to any changes in the lane configuration (for example, widening with an additional lane) during the design period and its impact on capacity and heavy vehicle growth rates.



7.5 Estimation of Traffic Load Distribution (TLD)

Addition

Refer to Appendix E for guidance on the estimation of traffic load distributions. Prior to using WIM data in pavement design, the relevance, accuracy and reliability of the data should be confirmed.

8 Design of flexible pavements

8.1 General

Addition

Layer thicknesses should be rounded up to the nearest 5 mm.

To allow for variations in construction thickness, a construction tolerance is typically added to the design thickness of the pavement as follows:

1. For unbound granular, modified granular and lightly bound pavements, a thickness of 20 mm is typically added to the design thickness.

2. For full depth asphalt, deep strength asphalt, flexible composite, AG(A) and ASt(A) pavements, 10 mm is typically added to the pavement course that governs the overall allowable loading.

3. For ASt(B) temporary pavements, 20 mm is typically added to the design thickness of the heavily bound (cemented) base course.

4. For foamed bitumen stabilised granular pavements, 15 mm is typically added to the thickness of the foamed bitumen stabilised material.

8.2 Mechanistic-empirical procedure

Addition

Mechanistic-empirical design is typically undertaken using the latest version of AustPADS or CIRCLY.

Thin interlayers and surfacings, such as sprayed seals and geosynthetics, are considered to be non-structural and therefore are not typically included in the design model.

For the design of pavements comprising foamed bitumen stabilised materials, the calculation of critical strains and the interpretation of results is consistent with the procedure for asphalt detailed in Tables 8.1 to 8.3 of AGPT02, and Sections 8.2.4 and 8.2.5 of AGPT02. Material input parameters for foamed bitumen stabilised materials are as detailed Section 6.7 of this supplement.

8.2.2 Procedure for elastic characterisation of selected subgrade and lime-stabilised subgrade materials

Difference

Lime stabilised subgrade materials

For lime-stabilised subgrade materials which have been designed according to Transport and Main Roads Technical Note TN151 Testing of Materials for Lime Stabilisation, the procedures for elastic characterisation are as detailed in Transport and Main Roads Technical Note TN74 Structural Design Procedure of Pavements on Lime Stabilised Subgrades.



Selected subgrade materials

For selected subgrade materials, sublayering is undertaken according to Steps 1 to 6 in Section 8.2.2 of AGPT02. However, to better reflect the structural contribution of these materials, an additional step is included prior to Step 1 for each selected subgrade material, as follows:

• For each selected subgrade material (commencing with the lowest selected subgrade material), calculate the thickness (T) using Equation 8.2.2. The thickness (T) is calculated such that the top sublayer of five equi-thick sublayers can achieve a vertical modulus equal to 10 times the design CBR of the material (up to a maximum 150 MPa).

𝑇𝑇 = 150log 2

log �𝐸𝐸𝐸𝐸 𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑖𝑖𝑚𝑚𝑚𝑚 𝑖𝑖𝑖𝑖 𝑚𝑚𝑡𝑡𝑡𝑡 𝑠𝑠𝑠𝑠𝑠𝑠𝑚𝑚𝑚𝑚𝑠𝑠𝑚𝑚𝑚𝑚𝐸𝐸𝐸𝐸 𝑠𝑠𝑖𝑖𝑢𝑢𝑚𝑚𝑚𝑚𝑚𝑚𝑠𝑠𝑖𝑖𝑖𝑖𝑢𝑢 𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑖𝑖𝑚𝑚𝑚𝑚

� (8.2.2)

• If the thickness of the selected subgrade material is less than T plus 100 mm, sublayering of the entire thickness of that material is undertaken according to Steps 1 to 6 in Section 8.2.2 of AGPT02.

• If the thickness of the selected subgrade material is at least T plus 100 mm, only the thickness T is sublayered into five equi-thick sublayers according to Steps 1 to 6 in Section 8.2.2 of AGPT02. The remaining overlying thickness of that material is not sublayered, and is instead assigned a vertical modulus 10 times the design CBR of the material (up to a maximum 150 MPa).

An example of this revised sublayering is shown in Figure 8.2.2. In the example, there is 600 mm of CBR 10% select fill overlying a subgrade with design CBR of 3%.

The left side of Figure 8.2.2 shows sublayering according to Section 8.2.2 of AGPT02. The right side of the figure shows the revised sublayering.

For the revised sublayering, T is first calculated using Equation 8.2.2, where Ev material in top sublayer is 100 MPa (10 times the CBR of the selected subgrade material), and Ev underlying material is 30 MPa (10 times the CBR of the subgrade). This results in T = 261 mm. As the thickness of this selected subgrade material is more than T plus 100 mm, only 261 mm of the material is sublayered according to Steps 1 to 6 in Section 8.2.2 of AGPT02. The remaining 339 mm of this material is not sublayered, and is instead assigned a vertical modulus of 10 times its design CBR, which in this case equals 100 MPa.



Figure 8.2.2 – Example of revised sublayering for selected subgrade materials

8.2.5 Procedure for determining allowable loading for asphalt, cemented material and lean-mix concrete

Addition

Where a mix-specific fatigue relationship is used in pavement design (determined as detailed in Section 6.5.11), Equation 44 in AGPT02 is replaced with the corresponding mix-specific equation as detailed in Transport and Main Roads Technical Note TN167 A New Approach to Asphalt Pavement Design.

8.2.8 Minimum support conditions under lightly bound, asphalt, heavily bound (cemented) and foamed bitumen stabilised pavements

New

Where the subgrade design CBR is less than 3%, the treatments detailed in Section 5.9 should first be applied, and a presumptive design CBR of 3% is adopted at the top of this treatment in the mechanistic-empirical design model.

Lightly bound base pavements

For lightly bound base pavements, the base is typically supported on a subbase with thickness of at least 150 mm and which achieves a vertical design modulus of at least 150 MPa at the top of the subbase (determined using the procedures detailed in Sections 8.2.2 and 8.2.3 of AGPT02).

This may be achieved by increasing the thickness of the subbase, and/or including additional select fill or unbound granular material beneath the subbase.

Asphalt and heavily bound (cemented) pavements

For asphalt and heavily bound (cemented) pavements with design traffic of 1000 ESA/day or more at opening, the improved layer (and any underlying layers) is typically designed to achieve a vertical design modulus at the top of the improved layer of at least 150 MPa (determined using the procedures detailed in Sections 8.2.2 and 8.2.3 of AGPT02).



This may be achieved by increasing the thickness of the improved layer, and/or including additional select fill or unbound granular material beneath the improved layer.

Foamed bitumen stabilised pavements

For pavements comprising foamed bitumen stabilised granular material, the improved layer (and any underlying layers) is typically designed to achieve a vertical design modulus at the top of the improved layer of at least 70 MPa (determined using the procedures detailed in Sections 8.2.2 and 8.2.3 of AGPT02).


8.3 Empirical design of granular pavements with thin bituminous surfacing

Addition

To reliably achieve an asphalt surfacing thickness less than 40 mm, the specified layer thickness would typically be 35 mm or less. This requires adoption of a 10 mm or smaller nominal size asphalt mix which may not be suitable in high speed (> 80 km/h) situations. Where such an asphalt surfacing is provided and the average daily ESA in the design lane in the year of opening exceeds 100, consideration should be given to adopting a minimum compaction standard of 102% (standard compaction) in the unbound base course to reduce the potential for asphalt fatigue.

8.3.1 Determination of basic thickness

Addition

The thickness design charts (Figures 8.4 and 12.2 in AGPT02) are based on the premise that pavement roughness at the end of the design period (the terminal roughness) will be three times the initial roughness. This is the standard typically adopted by Transport and Main Roads. For example, a terminal roughness of approximately 5.7 m/km can be expected, assuming that the initial roughness is 1.9 m/km.

However, if a higher ratio of terminal to initial roughness is accepted, a thinner pavement can be designed by adjusting the design traffic using Figure 8.3.1 which is based on NAASRA (1987b). Such an adjustment should only be considered following a project-specific assessment of the impacts of reduced pavement performance. This assessment should consider the consequences of premature distress, poor pavement performance, whole-of-life and road user costs, topographical factors and availability of pavement materials.

This procedure uses only roughness as an indicator of the effect of the reduced standard. For instance, it does not include other elements such as rut depth, volume change, safety or durability, which need to be independently assessed.

This reduced design standard procedure is typically only adopted in a very limited number of situations. Examples, subject to project-specific assessment, may include:

• staged construction

• special maintenance works which will be subsequently overlaid

• parking lanes

• low volume roads (for example, average daily ESA in the design lane in the year of opening < 100)



• pavements where environmental effects dictate performance, and

• temporary connections.

Figure 8.3.1 – Modified design traffic for an increased terminal roughness condition

9 Design of rigid pavements

9.2 Pavement types

9.2.2 Subbase types

Difference

Due to its proven ability to provide uniform support and erosion resistance, Transport and Main Roads has typically adopted lean-mix concrete subbase, even at traffic levels less than 1 x 107 HVAG. Transport and Main Roads has limited experience with other subbase types such as bound materials. These typically require a project-specific risk assessment (including whole-of-life cost comparison) and development of project-specific technical specifications.

In tunnels, project-specific requirements are typically required.

9.2.3 Wearing surface

Addition

Where the concrete base also functions as the pavement surfacing, diamond grinding may be required to meet surface property requirements.

The use of asphalt wearing surfaces over PCP and JRCP is not typically adopted as reflective cracking in the asphalt is likely from the underlying joints.

Where an asphalt wearing surface is required, CRCP in conjunction with a proprietary concrete surface primer, is typically used. In this case, future maintenance requirements should be considered, in particular the ability to mill the asphalt without unduly impacting on the concrete base.

1.0E+03

1.0E+04

1.0E+05

1.0E+06

1.0E+03 1.0E+04 1.0E+05 1.0E+06

Design Traffic (ESAs)

Mod

ified

Des

ign

Traf

fic (E

SAs)

3.04.05.06.0

Ratio Terminal/Initial

Roughness



9.3 Factors used in thickness determination

9.3.1 Strength of subgrade

Addition

Where the subgrade design CBR is less than 3%, the treatments detailed in Section 5.9 should first be applied, and a presumptive design CBR of 3% is then adopted in the determination of the equivalent subgrade design strength.

For concrete pavements with design traffic of 1000 ESA/day or more at opening, the improved layer (and any underlying layers) is typically designed to achieve an equivalent subgrade design strength of at least 5% (determined using Equation 55 of AGPT02).


9.4 Base thickness design

9.4.1 General

Addition

To allow for variations in the constructed layer thicknesses within the specified tolerances, a construction tolerance of 10 mm is typically added to the design base thickness.

An additional 10 mm should also be added to the base thickness in the following situations:

• For asphalt surfaced concrete, an additional 10 mm allowance should be provided to account for future fine milling and replacement of the asphalt surfacing. An alternative to this is the provision of an additional asphalt layer under the wearing surface so that future milling does not impact on the concrete base.

• Where concrete base is also the trafficked surface, an additional 10 mm allowance should be included to account for future surface grinding which may be necessary to improve functional characteristics such as ride quality, noise and texture. This allowance is not typically applied when future grinding is unlikely (for example, on roundabouts where vehicle speeds are relatively low and the geometry is such that grinding is not practical).

Project-specific requirements for fine milling and surface grinding are typically adopted to ensure suitable tolerances for these treatments are specified.

9.4.3 Minimum base thickness

Addition

Conformance with the minimum base thickness in Table 9.7 of AGPT02 is to be assessed after addition of 10 mm construction tolerance to the calculated design thickness. The additional grinding / milling tolerance should be added to the minimum base thickness.



10 Economic comparison of designs

10.1 General

Addition

For heavy-duty pavements, further guidance on comparison of alternative pavement types and configurations is provided in A Guide to the Whole-of-Life Costing of Heavy Duty Pavements (Main Roads, 1998).

10.7 Analysis period

Addition

An analysis period of 40 years is typically adopted by Transport and Main Roads.

11 Implementation of design and collection of feedback

11.2 Collection of feedback

11.2.1 Need

Addition

Users of this supplement are encouraged to provide feedback on pavement performance, particularly where atypical solutions are adopted, or where typical designs produce unsatisfactory performance. Feedback should be sent to the Principal Engineer (Pavement Design) for consideration in future updates.

12 Design of lightly trafficked pavements

12.4 Environment

12.4.2 Moisture

Addition

Unsealed shoulders

Unsealed shoulders are sometimes adopted on lightly-trafficked pavements where the consequences of moisture under the edge of the trafficked pavement can be tolerated. Where unsealed shoulders are to be considered, the following measures are typically adopted:

• extend the seal at least 200 mm beyond the delineated edge of the trafficked lane, and

• in the shoulder provide material with low permeability, low swell and sufficient strength to support limited traffic during periods of wet weather, ensuring that an undrained boxed condition does not result.

12.6 Pavement materials

12.6.1 Unbound granular materials

Addition

In drier parts of Queensland where traffic volumes are low, marginal or non-standard materials (also typically referred to as Type 4 materials) have been used extensively and many have performed satisfactorily. Use of such materials typically requires project-specific technical specifications be developed. These technical specifications should be based on local experience with the particular



material, including its construction and handling requirements, historic performance and future performance expectations for the project. The use of laboratory methods, such as the repeated load triaxial test, may assist in predicting the likely performance of these materials over a range of moisture conditions relative to standard materials.

Refer to the Transport and Main Roads Western Queensland Best Practice Guidelines for further information.

12.6.2 Cemented materials

Addition

Where non-standard unbound materials (such as Type 4) are incorporated into heavily bound (cemented) layers, their use is typically restricted to applications such as floodways on lightly-trafficked roads in relatively dry environments (where some additional resistance to moisture is desired). Controls on grading and plasticity index (or linear shrinkage) are typically required to reduce the potential for shrinkage cracking and improve uniformity.

Refer to the Transport and Main Roads Western Queensland Best Practice Guidelines for further information.



References

AS 2870-2011, Residential slabs and footings, Standards Australia, Sydney.

Austroads 2017, Guide to Pavement Technology, Part 2: Pavement Structural Design, AGPT02/17, Austroads, Sydney.

Austroads 2011, Guide to Pavement Technology Part 5: Pavement Evaluation and Treatment Design, AGPT05/11, Austroads, Sydney.

Austroads 2009a, Guide to Pavement Technology Part 3: Pavement Surfacings, AGPT03/09, Austroads, Sydney.

Austroads 2009b, Guide to Pavement Technology Part 10: Subsurface Drainage, AGPT10/09, Austroads, Sydney.

Austroads 2003, Control of moisture in pavements during construction, APRG Technical Note 13, Austroads, Sydney.

BTRE 2010, Road freight estimates and forecasts in Australia: interstate, capital cities and rest of state, Report 121, Bureau of Infrastructure, Transport and Regional Economics, Canberra, Australia.

Fox, E. 2002, Development of a map of Thornthwaite Moisture Index isopleths for Queensland, Australian Geomechanics: Journal and News of the Australian Geomechanics Society, Vol. 37, No. 3, June 2002.

Fox, E. 2000, A climate-based design depth of moisture change map of Queensland and the use of such maps to classify sites under AS 2870-1996, Australian Geomechanics: Journal and News of the Australian Geomechanics Society, Vol. 35, No. 4, December 2000.

Main Roads 1998, A Guide to the Whole-of-Life Costing of Heavy Duty Pavements, Queensland Department of Main Roads, Brisbane.

Main Roads 1988, Cement slurry applications to CTB layer bonding, Queensland Department of Main Roads, Brisbane.

NAASRA 1987a, Early findings of the ALF Beerburrum Trial, National Association of Australian State Road Authorities, Sydney.

NAASRA 1987b, Pavement Design, A Guide to the Structural Design of Road Pavements, National Association of Australian State Road Authorities, Sydney.

Transport and Main Roads 2018, Testing of Materials for Insitu Cement or Cementitious Blend Stabilisation, Technical Note TN149, Department of Transport and Main Roads, Brisbane.

Transport and Main Roads 2018, Testing of Materials for Insitu Foamed Bitumen Stabilisation, Technical Note TN150, Department of Transport and Main Roads, Brisbane.

Transport and Main Roads 2018, Testing of Materials for Lime Stabilisation, Technical Note TN151, Department of Transport and Main Roads, Brisbane.

Transport and Main Roads 2018, Testing of Materials for Plant-mixed Foamed Bitumen Stabilisation, Technical Note TN179, Department of Transport and Main Roads, Brisbane.

Transport and Main Roads 2017, A New Approach to Asphalt Pavement Design, Technical Note TN167, Department of Transport and Main Roads, Brisbane.



Transport and Main Roads 2017, Selection and Design of Sprayed Bituminous Treatments, Technical Note TN175, Department of Transport and Main Roads, Brisbane.

Transport and Main Roads 2017, Use of High Standard Granular (HSG) Bases in Heavy Duty Unbound Granular Pavements, Technical Note TN171, Department of Transport and Main Roads, Brisbane.

Transport and Main Roads 2016, Risk Management Framework, Department of Transport and Main Roads, Brisbane.

Transport and Main Roads 2015, Geotechnical Design Standard – Minimum Requirements, Department of Transport and Main Roads, Brisbane.

Transport and Main Roads 2015, High Modulus Asphalt (EME2) Pavement Design, Technical Note TN142, Department of Transport and Main Roads, Brisbane.

Transport and Main Roads 2015, Risk Management Organisational Policy, Department of Transport and Main Roads, Brisbane.

Transport and Main Roads 2015, Testing of Materials for Foamed Bitumen Stabilisation, Technical Note TN150, Department of Transport and Main Roads, Brisbane.

Transport and Main Roads 2014, Engineering Innovation in the Department of Transport and Main Roads, Department of Transport and Main Roads, Brisbane.

Transport and Main Roads 2012, Pavement Rehabilitation Manual, Department of Transport and Main Roads, Brisbane.

Transport and Main Roads 2012, Structural Design Procedure of Pavements on Lime Stabilised Subgrades, Technical Note TN74, Department of Transport and Main Roads, Brisbane.

Van der Merwe, D. H. 1964, The prediction of heave from the plasticity index and percentage clay fraction of soils. The Civil Engineer in South Africa, Volume 6, South African Institute of Civil Engineers, South Africa.



Appendices

Appendix E Characteristics of traffic at selected WIM sites

Addition

E.1 Introduction

This appendix provides guidance on the selection and derivation of Traffic Load Distributions (TLDs) for use in pavement design. While TLDs are readily available from Weigh-In-Motion (WIM) data, there is a limited number of WIM sites in Queensland. Hence, in many cases, assumptions will be required to select or derive a TLD so that pavement designs can be undertaken.

One of the key features of this appendix is the introduction of an analytical method that combines vehicle class-specific TLDs with classified vehicle counts (or estimates) for the project site. The Austroads 12-bin classification system is adopted in this appendix, as detailed in Table 7.1 of AGPT02.

A spreadsheet that accompanies this appendix is available from https://www.tmr.qld.gov.au/business-industry/Technical-standards-publications/Pavement-design-supplement.

E.2 Methods for selecting or deriving TLDs for pavement design

This appendix describes a hierarchy of methods for selecting or deriving TLDs, as shown in Figure E.2.

Figure E.2 – Hierarchy for selecting TLDs

The highest level of confidence is expected at the top of the hierarchy, with confidence reducing down the hierarchy. A method commensurate with the importance of the project, availability of relevant data, and resources available for data collection should be adopted.

The methods in this appendix are based on the use of data for existing heavy vehicles. Where future changes are expected, such as changes to axle loads and/or proportions of vehicles within each vehicle class, the procedures should be tailored to the specific circumstances.

It is typical practice to impose an upper limit on the loads determined from WIM measurements to remove small proportions of potentially spurious values that can have a disproportionate impact on pavement designs. The method for adjusting TLDs to remove these values is detailed in Section E.6.

The methods for selecting or deriving a TLD are detailed in the following sections.

E.3 Method 1: TLD from WIM site at or near the project location

A TLD from the project site generally provides the highest level of confidence. This data should be used where there is an existing WIM site at or near the project location, or where a temporary WIM site is used to collect data for the project.

Method 1: TLD from WIM site at or near the project location

Method 2: Class-specific TLDs from relevant WIM site combined with project specific classified vehicle count

Method 3: Presumptive class-specific TLDs combined with project specific classified vehicle count

https://www.tmr.qld.gov.au/business-industry/Technical-standards-publications/Pavement-design-supplement

https://www.tmr.qld.gov.au/business-industry/Technical-standards-publications/Pavement-design-supplement



This method is also suitable where there is no WIM data from the project location, but the mix of traffic (vehicle types and loads) at the project location is similar to that at a selected WIM site.

TLDs from Transport and Main Roads WIM sites are available from TSDM (refer to Section 7.4.4). These TLDs should be adjusted using the method detailed in Section E.6.

When Method 1 is selected, a more advanced analysis of the WIM site data may be undertaken in some cases. Where a more advanced analysis is to be undertaken, designers are referred to the additional notes on Method 1 in Section E.7.

E.4 Method 2: Class-specific TLDs from relevant WIM site combined with project specific classified vehicle count

This method should be used where there is no WIM site located at or near the project. This method requires the following data:

• classified vehicle count (or estimates) at or near the project

• class-specific TLDs from a relevant WIM site.

In this method, 10 class-specific TLDs are required, comprising one TLD for each vehicle class from Class 3 to Class 12. These class-specific TLDs are combined at the proportions determined from the classified vehicle count to provide an overall TLD for use in pavement design calculations.

The WIM site considered most relevant to the project location should be selected.

The spreadsheet that accompanies this appendix includes a list of Transport and Main Roads WIM sites, and class-specific TLDs for each site. The spreadsheet can be used to derive an overall TLD by combining class-specific TLDs at the classified vehicle count proportions.

E.5 Method 3: Presumptive class-specific TLDs combined with project specific classified vehicle count

This method is identical to Method 2 described in Section E.4, except it uses presumptive class-specific TLDs rather than values from a relevant WIM site.

This method provides the lowest level of confidence and generally should only be used for low risk sites and/or where no reasonable alternative option is available. The designer should consider the suitability of this method, noting that specific site characteristics may deem this method unsuitable. For example, the presumptive class-specific TLDs may not be suitable for sites with a high proportion of loaded cattle, quarry or mine haulage vehicles.

This method requires the following data:

• classified vehicle count (or estimates) at or near the project

• presumptive class-specific TLDs.

The spreadsheet that accompanies this appendix includes presumptive class-specific TLDs which have been derived from an analysis of Queensland WIM data.

To improve the confidence in the use of Method 3, Transport and Main Roads Districts and their design consultants should use local information to develop presumptive class-specific TLDs for use on specific routes in their local areas.



E.6 Upper limit on WIM loads

Small proportions of spurious loads are typically removed from TLDs as these loads can have a disproportionate impact on pavement designs. The procedure for removal of spurious loads is only intended for limited data removal (up to a few percent of HVAGs), otherwise further more detailed analysis of the WIM data is needed to validate it before it is used in pavement design.

HVAG proportions for loads that are greater than the loads listed in Table E.6 are typically removed. The remaining HVAG proportions in the TLD should then be increased so that, for each HVAG type, the sum of the remaining proportions does not change from its original value.

Table E.6 – Upper limit on WIM loads

HVAG Type Upper Limit on WIM Load (kN)

SAST 90

SADT 180

TAST 170

TADT 330

TRDT 400

QADT 480 E.7 Additional notes on Method 1

When adopting Method 1, pavement designers should recognise that the definition of heavy vehicles used at Transport and Main Roads permanent WIM sites differs from the definition used in AGPT02 for calculating pavement design traffic.

AGPT02 defines heavy vehicles based on vehicle classification, where all Class 3 and above vehicles are considered to be heavy vehicles. This definition is typically used to quantify the percentage of heavy vehicles (%HV) used to estimate the pavement design traffic (NDT).

Conversely, at Transport and Main Roads permanent WIM sites heavy vehicles are defined as those with a gross mass of 4.5 tonnes or above, and data for vehicles with gross mass less than 4.5 tonnes is not captured.

Hence, use of a TLD from a WIM site (which ignores vehicles less than 4.5 tonnes) together with the %HV from a classified vehicle count (which does include vehicles less than 4.5 tonnes) will usually lead to overestimation of the pavement design traffic. This overestimation may be accepted or may be corrected for. Where it is decided to correct for the overestimation, the procedure detailed in Method 2 should be followed.

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